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Part III: Travel Demand Modeling

10 First Step of Four Step Modeling (Trip Generation)

Chapter Overview

The previous chapter introduces the four-step travel demand model (FSM), provides a real-world application, and outlines the data required to carry out each of the model steps. Chapter 10 focuses on the first step of the FSM, which is trip generation. This step involves predicting the total number of trips generated by each zone in a study area and the trips attracted to each zone based on their specific purpose. The chapter delves deeper into this process, providing detailed insights into the factors influencing trip generation and how they can inform transportation planning decisions. Trip generation is a function of land use, accessibility, and socioeconomic factors, such as income, race, and vehicle ownership. This chapter also illustrates how to incorporate these inputs to estimate trips generated from and attracted to each zone using regression methods, cross-classification models (tables), and rates based on activity units as specified by the Institute of Transportation Engineers (ITE). It also provides examples to demonstrate the model applications.

The essential concepts and techniques for this step, such as growth factors and calibration methods, are also discussed in this chapter.

Learning Objectives

Student Learning Outcomes

• Explain what trip generation is and summarize what factors contribute to trip generation.
• Recognize the data components needed for trip generation estimation and ways to prepare them for estimation.
• Summarize and compare different methods for conducting trip generation estimation and ways to interpret their results

Introduction

The Four-Step Model (FSM) is comprised of four consecutive steps, each addressing a specific question, ultimately contributing to an enhanced comprehension of travel demand. The questions are:

• Trip generation (Chapter 10) – How many total trips are estimated? What is the demand (total trips)?
• Trip distribution (Chapter 11) – Where are the trip destinations? What are the destinations of the trips?
• Modal split (Chapter 12) – What modes are used to complete those trips?
• Trip assignment (Chapter 13): What routes will be selected to complete the trips? (Meyer, 2016).

Figure 10.1 shows how the model is structured. It shows what kinds of data we provide as input for the model, and what steps we take to generate outputs.

Key Concepts

Link-diverted trips: Trips produced as a result of congestion near the generator and require a diversion; new traffic will be added to the streets adjacent to the site. In other words, these are trips with multiple destinations within one area and do not require road access between destinations.

Diverted trips:  Travel changes in time and route are known as diverted trips. For example, when a trip is diverted or re-routed from the original travel path due to the traffic on nearby roadways, new traffic on surrounding streets results, but the trip attraction remains the same.

Pass-by trips (see below) do not include link-diverted trips.

Pass-by trips: This type of trip is described as a trip for which the destination is not a final but a stop along the way by using the connecting roads. Passing-by traffic volume in a zone depends on the type and size of development or available activities.  A gas station with higher prices near an employment center may receive many pass-by trips for gas compared to other gas stations (Where up to 50 % of all trips to a service station are travelers passing by rather than people who made a special trip to the gas station)

A gas station located in close proximity to an employment center and charging higher prices might experience a higher number of pass-by trips for gas, in contrast to other gas stations. It is observed that up to 50% of all trips to a service station are by travelers passing by, rather than individuals specifically making a deliberate trip to that gas station.  (Meyer, 2016).

Traditional FSM Zonal Analysis   : After inputting the required data for the model, FSM calculates the number of trips generated by or attracted to each zone using the primary input using data from travel surveys from census data. While one limitation of the trip generation model is reduced accuracy due to aggregated data, the model offers a straightforward and easily accessible set of data requirements. Typically, by utilizing basic socio-economic information like population, job figures, vehicle availability, income, and similar metrics, one can calculate trip generation and distribution.

 Activity-based Analysis: There are also other (newer) methods for travel demand modeling in which individual trips are modeled based on individuals’ behaviors and activities in a disaggregated manner. The methods that use activity-based models can estimate travel demand based on a basic premise—the demand to accomplish personal activities during the day (for example, work, school, personal business, and so forth) produces a demand for travel that is often connected (Glickman et al., 2015). However, activity-based models have extensive data requirements as individuals, rather than traffic analysis zones, are the unit of analysis. Detailed information on each individual’s daily activity and socioeconomic information is needed.

Travel diaries (tours) are one source of such information (Ettema et al., 1996; Malayath & Verma, 2013). Because of travel demand modeling, additional information can be learned about the study area. For example, the detailed data may reveal information about areas with or without minimum accessibility, underserved populations, transportation inequity, or congested corridors (Park et al., 2020).

Several scholars have compared the two models – traditional zonal models and activity-based models – to assess factors such as forecasting ability, accuracy, and policy sensitivity. Despite initial expectations, the findings from some studies show no improvement in the accuracy of activity-based models over traditional models (Ferdous et al., 2011). However, considering the complexity of decision-making, activity-based models can be used to minimize the unrealistic assumptions and aggregation bias inherent in FSM models. Still, the applicability and accuracy of activity-based models should be independently assessed for each context analysis to determine which is the most effective approach.

In transportation analysis, trips are typically classified based on the origin (O)and destination (D) location. As mentioned in previous sections, for a more accurate and better estimation of trip generation results, it would be better to identify a wide range of trip categories and have disaggregate results by trip purposes. The following lists typical trip classifications:

• Home-based work (HBW) : If one of the trip origins is home and the destination is the workplace, then we can define the trip purpose as home-based work (HBW). These trips usually happen in the morning (to work) and in the evening (from work to home).
• Home-based non-work (HBNW) : If from the two ends of the trips, one is home and the other one is not workplace, the trip purpose is home-based-non-work (HBNW). Sometimes this trip purpose is called home-se is called home-based other ( HBO ). Examples of these are going to services like a restaurant or hospital.
• Non-home-based (NHB) : If neither the origin nor the destination is home, we can classify the trip as a non-home-based (NHB) purpose. One typical example is a lunch break trip from the workplace to a shopping mall.

While the above categories include only one origin and one destination, most individual trips are more complex due to chaining different trips into one tour. For instance, a person may stop for coffee or drop their child at daycare on the way to work, leave on lunch break for shopping, and then pick up their child from daycare on the way home. A tour is a continuous chain of trips an individual takes daily to complete their chores, which activity-based models can simulate (Ben-Akiva & Bowman, 1998).  Figure 10.2 illustrates the different trip purposes and differences between FSM and activity-based models in trip classification.

It is important to note that home-based trips can be work, school, shopping, recreational, and others. While the first two are usually mandatory and made daily, the rest are less regular or discretionary.

Trips can also be classified based on the time of day that they are generated or attracted, as traffic volumes on various corridors vary throughout the day. Essentially, the proportion of different trip purposes in the total trips is more pronounced during specific times of the day, usually categorized as peak and off-peak hours (Alkaissi, 2021).

Lastly, another factor to consider is the socio-economic characteristics and behaviors of the trip makers. An understanding of these factors is crucial for classifying trips, as some possess significant influence on travel behavior (Giuliano, 2003; Jahanshahi et al., 2009; Mauch & Taylor, 1997), such as, income level, car ownership, and household size.

Trip generation

Recall from the previous chapter, a comprehensive analysis of travel demand should include trip generation and attractions for different zones. These values should be balanced to produce an equal number of trips. In general, trip generation helps predict the number of trips for different purposes generated by and attracted to every zone in a study area.

Additionally, the number of trip ends – the total number of trips entering and leaving a specific land use or site over a designated period – can be calculated in the trip generation step (New Jersey Transit, 1994). Despite recent trends for remote work, most people do not live and work in the same area. Daily round trips to work or shopping centers originate from different locations. In this regard, the distribution of activities, like job centers, can help us to understand daily travel patterns (Wang & Hofe, 2020).

After generating an overview of the distribution of activities and land uses, we must identify the factors or conditions affectingtripgeneration. Over the years, studieshaveexaminedfactorsthatarenow accepted as standard:income,autoownership,familysize,ordensity(Ewingetal.,1996;Sharpeetal.,1958).Using a zonal level analysis, population, number of jobs, and availability of modes can affect trip generation (Wang&Hofe,2020).Similarly,thetypeandsizeofretailstores canalsoaffectthenumberoftrips.

Additionally, the predominant travel mode chosen by the population for their daily trips is a vital factor to consider. Because of the interconnectedness of land use and transportation, the primary mode influences the distribution of services, employment centers, and the overall structure and boundaries of the city. In summary, the type and intensity of land use in combination with transportation mode play crucial roles in trip generation.

The table below shows 5 hypothetical cities where the predominant mode of transportation is different for each case. According to the speed of each mode, the extent to which activities are dispersed, determines the size of the city. For instance, a city where rail is the frequent mode of transportation, the speed (21 mph) and travel time (43 mins), the catchment (distance) would be 12 miles. Using this distance as a radius, we can estimate the size of the city.

Table 10.1 Hypothetical cities with different transportation modes

Note. Table created by authors.

According to the discussion here, the following categories can be identified as contributors to trip generation (McNally, 2007).

• Land-use types
• Land-use Intensity
• Location/accessibility
• Travel time
• Travel mode (transit, auto, walking …)
• Households’ income level
• Auto ownership rate
• Workers per household

Trip Generation Calibration

Traffic Analysis Zones (TAZs) connected by transportation networks and facilities are used to model the study area. TAZs are the smallest units of analysis in FSM. They are typically bounded by transportation networks or natural boundaries such as rivers.

Prior to estimating trip generators and attractions, calibrate the model as follows:

• Determine the regional population and the employment rate for the forecasting year to estimate the total number of interactions and possible future patterns.
• Allocate population and economic activities to each TAZ to prepare the study area for the modeling framework.
• Specify the significant variables and a proper method for creating the travel demand model (trip generation step). This step can be called model specification.

Calibration is an essential process in travel demand modeling. It involves collecting actual traffic flow data and calculating model parameters to verify the accuracy of the model for a specific region. The purpose of calibration is to match predicted outcomes with observed data, ensuring that model results are reliable and trustworthy (Wang & Hofe, 2020).

FSM MODELING UNITS

As discussed previously, the unit of analysis used for the model varies by model type.  The unit of analysis is important as it guides data collection. Traditional zonal analysis, like FSM, typically uses TAZs.  Activity-based models typically use data at the level of the individual person or household. There are three general methods for trip generation estimations:

1.     Growth factor model,

2.     regression methods,

3.     cross-classification models (tables),

4.     and rates based on activity units (ITE).

Generally, the trip generation step requires two types of data – household-based and zonal-based. Household-based data is more suitable for cross-classification analysis , and zonal-based data is more applicable for regression method analysis (the following sections will discuss these methods).

The third method is based on rates by which each land use type generates trips. The very general process for this method is identifying land use types, estimating trip generation according to ITE manuals, calculate total generation, and finally modifying based on specific characteristics such as proximity or location of land use. In this chapter, we do not wish to illustrate the third model, instead we focus on regression and cross-classification models since they are more data-oriented methods, more realistic and more frequently used in real-world.

The zonal analysis consists of areas divided into smaller units (zones), from which an estimate of trips generated in each zone is obtained (aggregate model). Household-based analysis decomposes zones into smaller units based on households with similar characteristics. In transportation travel demand modeling, we estimate zonal trips for various purposes, such as work, school, shopping, and social or recreational trips. As said, a zone is an area with homogeneous characteristics of land use, population, income, vehicle ownership, and the same access path outside of the zone.

In many cases, however, sufficient data at this resolution is unavailable (available at Census Tracts, Blocks, and Block Groups). In these conditions, the modeler should assess if the lower-resolution data is sufficient for their purpose. If not, using appropriate GIS-based data conversion methods, the data from a higher level (such as Census Tract) can be migrated to lower-level units (such as TAZ).

GROWTH FACTOR MODELING

A straightforward approach for estimating future trip generation volumes is to translate trends from the past into the future based on a linear growth trend of effective factors such as population or income. This method projects past data into the future by assuming a constant growth rate between two historical points. We can use this method when trip production and attraction in the base year are available, but the cost function (like travel time) is not. While this method is commonly used, it is important to note that it is insensitive to the distance between zones, which affects the estimated future data (Meyer, 2016).

In this model, the future number of trips equals the number of current trips times the growth factor.

Equation below is the method’s mathematical format:

T i is the number of trips in the zone in the forecasting year

t i is the current number of trips in that zone

f i is a growth factor

The growth factor itself consists of a number of explanatory variables that we acknowledge have impact on trip generation such as population, income (I), and ownership (V). To calculate a single growth factor with all these variables, the below equation is useful:

P i d is the population in the design year

P i c is the population in the current year

I i d is the income level in the design year

I i c is the income level in the current year

V i d is the vehicle ownership rate in the design year

V i c is the vehicle ownership rate in the current year

In a small neighborhood, 630 households reside, out of which 300 households have cars and 330 are without cars. Assuming population and income remain constant, and all households have one car in the forecasting year, calculate the total trips generated in the forecasting year and the growth factor (trip generation rate for 1-car: 2.8; 0-car:1.1). Assume that a zone has 275 households with cars and 275 without cars, and the average trip generation rates for the two groups are 5.0 and 2.5 trips per day.

Assuming all households will have a car in the future, find the growth factor and the future generated trips from that zone, keeping population and income constant.

• Current trip rate ti=300 × 2.8 + 330 × 1.1 = ? (Trips/day)
• Growth factor Fi=Vdi/Vc =630/300= ?
• Number of future trips Ti = Fiti = 2.1 × 1203 = ? (Trips / day)

Regression Analysis

Regression analysis begins with the classification of populations or zones using the socio-economic data of different groups (like low-income, middle-income, and high-income households). Trip generation can be calculated for each category and the total generated trips by each socio-economic group such as income groups and auto ownership groups using linear regression modeling. The reason for disaggregating different trip making groups is that as we discussed, travel behavior can significantly vary based on income, vehicle availability and other capabilities. Thus, in order to generate accurate trip generations using linear models such as OLS (Ordinary Least Squares) regression, we have to develop different models with different trip making rates and multipliers for different groups. This classification is also employed in cross-classification models, which is discussed next. While the initial process for regression analysis is similar to cross-classification models, one should not confuse the two methods, as the regression models attempts to fit the data to a linear model to estimate trip generation, while cross-classification disaggregates the study area based on characteristics using curves and then attributes trips to each group without building predictive models.

Alternatively, the number of total trips attracted to each zone would be determined using regression analysis on employment data and land-use attraction rates. The coefficients for the prediction model in linear regression analysis can be derived. The prediction model has a zone’s trip production or attraction as a dependent variable, and independent variables are socio-economic data aggregated by zone. Below, we illustrate a general formula for the regression type analysis:

Trip Production= f (median family income, residential density, mean number of automobiles per household)

The estimation method in this regression analysis is OLS (Ordinary Least Squares). After zonal variable data for the entire study area are collected, linear regression analysis is applied to derive the coefficients for the prediction model. A major shortcoming associated with this model is that aggregate data may not reflect the precise effect of data on trip production. For instance, individuals in two zones with an identical vehicle ownership rate may have very different access levels to private cars, thus having different trip productions. The cross-classification model described in the next section helps address this limitation (McNally, 2007).

Equation below shows the typical mathematical format of the trip generation regression model:

where X i is the independent variable and a i is the associated coefficient.

In a residential zone, trip production is assumed to be explained by the vehicle ownership rate of households. For each household type, the trip-making rates are shown in Table 10.2). Using this information, derive a fitted line. Table 10.2 documents 12 data points. Each corresponds to one family and the number of trips per day. For instance, for a 1-vehicle family, we have (1,1) (1,3), and (1,4).

Table 10.2 Sample vehicle ownership data for trip generation

Note. adapted from “Introduction to transportation engineering” by T.V. Mathew and K. K. Rao, 2006 ( https://www.civil.iitb.ac.in/tvm/2802-latex/demo/tptnEngg.pdf ), copyright 2023 CDEEP IIT Bombay.

The linear equation will have the form: y = bx + a. Where: y is the trip rate, and x is the household vehicle ownership, and a and b are the coefficients. For a best fit, b is given by the equation:

Based on the input table, we have:

Σx = 3 × 1 + 3 × 2 + 3 × 3 + 3 × 4 = 30 Σx2 = 3 × (12) + 3 × (22) + 3 × (32) + 3 × (42) = 90 Σy = 8 + 14 + 21 + 28 = 71 Σxy = 1 × 1 + 1 × 1 + 1 × 3 + 1 × 3 + 2 × 3 + 2 × 4

y‾ = 71/12 = 5.91 x‾ = 30/12 = 2.5 b = (nΣxy − ΣxΣy)/[(nΣx2 − (Σx)2] =((12 × 209) − (30 × 71))/((12 × 90) − (30)2) = 2.1 a = y‾ − b x‾ = 5.91 – 2.1 × 2.5 = +0.66 y= 2.1X + 0.66

Cross Classification Models

This type of model estimates trip generation by classifying households into zones based on similarities in socio-economic attributes such as income level or auto ownership rate. Since the estimated values are separate for each group or category of households, this model aligns with our presumption that households with similar characteristics are likely to have similar travel patterns (Mathew & Rao, 2006). The first step in this approach is to disaggregate the data based on household characteristics and then calculate trip generations for each class. Aggregate all calculated rates together in the final step to generate total zonal trip generations. Typically, there are three to four variables for household classification, and each variable includes a few discrete categories. This model’s standard variables or attributes are income categories, auto ownership, trip rate/auto, and trip purpose.

The cross-classification method involves grouping households based on different characteristics such as income and family size. For each group, the trip generation rate can be calculated by dividing the total number of trips made by families in that group by the total number of households in that group within each zone (Aloc & Amar, 2013).

The following are some of the advantages of the cross-classification model:

• Groupings are independent of the TAZ system of the study area.
• No need to assume linearity as it disaggregates the data.
• It can be used for modal split.
• It is simple to run and understand. Furthermore, some of the model’s disadvantages are:
• It does not permit extrapolation beyond its calibration strata.
• No measure of goodness of fit is identifiable.
• It requires large sample sizes (25 households per cell); otherwise, cell values will vary.

After exploring the general definitions and features of the cross-classification model for trip generation estimations, we present a specific example and show how to perform each model step in detail.

Suppose there is a TAZ that contains 500 households, and the average income for this TAZ is

$35000. We are to develop the family of cross-classification curves and determine the number of trips produced by purpose. The low, medium, and high income are $15,000, $25,000, and $55,000, respectively (Note: this data is extracted from 1990 and is therefore out of date. Current rates for income categories may be higher.) (Adapted from: NHI, 2005). For the first step, we should develop the family of cross-class curves for the income levels and find the number of households in each income category.

If we divide the households by six income ranges, we have the table below, derived from the survey.

Based on this table, we can plot the curves in the following format:

If you look at the vertical line on the $40,000 income level, you can find that the intersection of this line with three income range categories shows the percentage of households in that range. Thus, to find the number of total households in each group we have to find the intersection of the curves with average income level ($35,000). In the above plot, the orange line shows these three values, and the table below can be generated according to that:

2. In the second step, after deriving the number of households in each income category, we follow the same procedure for other variables: vehicle ownership. In other words, now we find trips per household in each auto ownership/income group “class.” Again, from the survey, we have the following table, and we can generate the plot of the curves according to that:

Like the previous step, the intersection of four auto ownership curves with low, medium, and high-income level lines determine the share of each auto ownership rate in each income level group:

3. After calculating the number of households in each income level category and auto ownership rate, the next step in the trip generation estimation procedure is to find the number of trips per household based on income level and auto ownership rate. The table below shows the trip generation rate for different income levels:

In Figure 10.3, the meeting point of three income levels and auto ownership status with trip rates yields us the following table:

4. In the fourth step, we must incorporate the trip purpose into the model. To that end, we have trip purposes ratios based on income level from the survey. Like the previous steps, we plot the table on a graph to visualize the curves and find the intersection points of the curves with our three low, medium, and high-income levels:

Based on the findings of this plot, we can now generate the table below, in which the percentage of trips by purpose and income level is illustrated:

Now, we have all the information we need for calculating the total number of trips by household income level and trip purpose.5.

5. In the next step, we calculate the total number of households in each income group based on the number of cars they own. Multiplying the number of households in each income group (00) to the percent of families with a certain number of cars (A) will give us the mentioned results.

6. Once we have the total number of households in each group of income based on auto ownership, we multiply the results to the trips rate (B) so that we have the total number of trips for each group.

7. In the next step, we sum the results of the number of trips by the auto ownership number to have the total number of trips for each income group (∑(00xAxB)).

8. Finally, the results from the above table (416, 3474, 1395) will be multiplied by the percentage of trip purposes for each income group in order to estimate the number of trips by trip purposes for each income group. The table below shows these results as the final trip generation results (example adapted from: NHI, 2005).

Cx∑(00xAxB):

Note. This example was adapted from Traffic and Highway Engineering by N.J. Gaber and L. A. Hoel, 1999, p.545 Pacific Grove, CA: PWS-Kent Publishing Co. Copyright 1997 by PWS-Kent Publishing Co.

Trip Attraction in the Cross-Classification Model

In the previous section, we modeled trips generated from different households and zones, and calculated their total number by purpose. However, in trip generation, trip attractions play a crucial role, along with trip production. To measure the attractiveness of zones, we can use an easy and straightforward method, which is to determine the size of each zone and the land use types within it, such as square feet of floor space or the number of employees. We can then derive trip generation rates for different attractions from surveys. Trip attractions refer to the number of trips that end in one zone. Typically, we express trip generation rates for different attractions in terms of the number of vehicle trips per household or unit area of non-residential land use. For instance, Table 10.13 provides trip attraction rates for residential and some non-residential land uses. The number 0.074 for HBW trips means that each household can attract 0.074 HBW vehicle trips per day. For non-residential land uses, the numbers are also dependent on the type and size of land uses. As shown in Table 10.13, the retail sector is more attractive than the basic sector.

Table 10.13 shows that the retail sector is more attractive than the basic sector.

Note. Table created by authors

After collecting the necessary data from surveys or other appropriate sources, a regression analysis can be used to determine the attraction rates for each land-use category. Then, the HBW vehicle trips attracted to a zone are then calculated as:

TA HBW_H = home-based work vehicle trip attractiveness of the zone by households

N hh = number of household in the zone

TAR _R = trip attraction rate by households

In a similar way, the HBW trips attracted by retail are calculated from the size of retail land use and the retail trip attraction rates.

TA HBW_NR = home-based work vehicle trip attractiveness of the zone

A _NR = non-residential land use size in the zone

TAR _NR = trip attraction rate of the non-residential land use

Assume that Table 10-14 is derived from survey data in a hypothetical city and attractiveness of each land use by trip purpose is generated.

Note. Table was adapted from Traffic and Highway Engineering by N.J. Gaber and L. A. Hoel, 1999, p.600 Pacific Grove, CA: PWS-Kent Publishing Co. Copyright 1997 by PWS-Kent Publishing Co

Additionally, a new retail center in a part of the city accommodates 370 retail workers and 550 non-retail workers. According to this information, the number of trips attracted to this area can be calculated as:

First, using the information in table 10.14:

HBW: (370 * 1.7) + (550 * 1.8) = 1619

HBO: (370 * 5.4) + (550 * 2.2) = 3208

NHB: (370 * 3.0) + (550 * 1.1) = 1715

Total = 6542trips/day (example adopted from: Alkaissi, 2021)

Balancing Attractions and Productions

After generating trips, the final step is to balance trip production and attraction. Since trip generation is more accurate, and its validity is more reliable compared to trip attraction models, attraction results are usually brought to the scale of trip generation. Balance factors are used to balance Home-Based Work (HBW) trip attraction and production, which is illustrated in the example below.

Note. Table was adapted from Traffic and Highway Engineering by N.J. Gaber and L. A. Hoel, 1999, p.602 Pacific Grove, CA: PWS-Kent Publishing Co. Copyright 1997 by PWS-Kent Publishing Co.

According to Table 10.15, the total number of trips generated by all three zones is 600. However, the total number of trips attracted to all the zones is 800, which is an unreasonable value. To fix this issue, we use a balancing factor to multiply each cell in the attraction column by (600/800).

When planning NHB (non-home-based) trips, it is important to take an extra step to ensure that the production and attraction outputs are balanced. This means that for all zones and each zone, the total number of trips attracted and generated should be the same. The reason for this is that NHB trips have unknown origins, meaning that the origin information is not available through surveys or census data. Therefore, the most accurate estimate possible is to set the total NHB productions and attractions to be equal.

In this chapter, we introduced and reviewed the first step of travel demand modeling that is developed for estimating trip generation from each neighborhood or zone. We specifically focused on different methods (growth factor, regression, and cross-classification) and provided examples for each method along with an overview of key concepts and factors contributing to trip generation. Today, the ongoing advancements in computational capacity as well as capabilities for real-time data collection appear to be promising in equipping us with more accurate predictions of trip generation. For instance, GPS mobile data can be used to empirically estimate the rate of trip generation, build advanced models (such as machine learning models) to develop highly calibrated and optimized models.

In the next chapter, we learn about trip distribution. It is worth noting here that the trip distribution is completely based on a foundation of attractiveness of various location determined in trip generation step. As we will see, we used gravity-based models to allocate demand to pair of zones in space. In other words, four-step model is a sequential model, in which the accuracy and reliability of the each step depends on model performance in previous steps.

• activity-based model is travel forecasting framework which is based on the principle that travel is derived from demand reflected in activity patterns of individuals.
• Travel diaries (tours) refers to a chain of trips between multiple locations and for different purposes such as home to work to shopping to home.

Land-use Intensity is a measure of the amount of development on a piece of land usually quantified as dwelling per acre.

• Pass-by trips refers to the trips for which the destination is not a final destination but rather an stop along the way by using the connecting roads.
• Diverted link trips are produced from the traffic flow in the adjacent area of the trip generator that needs diversion. This new traffic will be accumulated in the roadways close to the site.

Key Takeaways

In this chapter, we covered:

• What trip generation is and what factors influence trip generation.
• Different approaches for estimating trip generation rates and the data components needed for each.
• The advantages and disadvantages of different methods and assumptions in trip generation.
• How to perform a trip generation estimation manually using input data.

Prep/quiz/assessments

• List all the factors that affect trip generation. What approaches can help incorporate these factors?
• What are the different categories of trip purposes? How do newer (activity-based models) models differ from traditional models (FSM) based on trip purposes?
• What are the data requirements for the growth factor model, and what shortcomings does this method have?
• Why should trip productions’ and attractions’ total be equal, and how do we address a mismatch?

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Jahanshahi, K., Williams, I., & Hao, X. (2009). Understanding travel behaviour and factors affecting trip rates. In  European Transport Conference, Netherlands (Vol. 2009). https://www.researchgate.net/profile/Kaveh Jahanshahi/publication/281464452_Understanding_Travel_Behaviour_and_Factors_Affecting_Trip_Rates/links/57286bc808ae262228b5e362/Understanding-Travel-Behaviour-and-Factors-Affecting-Trip-Rates.pdf

Malayath, M., & Verma, A. (2013). Activity based travel demand models as a tool for evaluating sustainable transportation policies. Research in Transportation Economics , 38 (1), 45–66. https://doi.org/10.1016/j.retrec.2012.05.010

Mathew, T. V., & Rao, K. K. (2006). Introduction to transportation engineering. Civil Engineering–Transportation Engineering. IIT Bombay, NPTEL ONLINE, Http://Www. Cdeep. Iitb. Ac. in/Nptel/Civil% 20Engineering .

Mauch, M., & Taylor, B. D. (1997). Gender, race, and travel behavior: Analysis of household-serving travel and commuting in San Francisco bay area. Transportation Research Record , 1607 (1), 147–153.

McNally, M. G. (2007). The four step model. In D. A. Hensher, & K. J. Button (Eds.), Handbook of transport modelling , Volume1 (pp.35–53). Bingley, UK: Emerald Publishing. http://worldcat.org/isbn/0080435947

Meyer, M. D., (2016). Transportation planning handbook . John Wiley & Sons: Hoboken, NJ, USA, 2016.

New Jersey Transit, N. (1994). Planning for transit-friendly land use: A handbook for New Jersey communities . NJ Transit, Trenton, NJ.

NHI. (2005). Introduction to Urban Travel Demand Forecasting . In National Highway Administration (Ed.), Introduction to Urban Travel Demand Forecasting. American University. . National Highway Institute : Search for Courses (dot.gov)

Park, K., Sabouri, S., Lyons, T., Tian, G., & Ewing, R. (2020). Intrazonal or interzonal? Improving intrazonal travel forecast in a four-step travel demand model. Transportation , 47 (5), 2087–2108. https://doi.org/10.3141/1607-20

Sharpe, G. B., Hansen, W. G., & Hamner, L. B. (1958). Factors affecting trip generation of residential land-use areas . Highway Research Board Bulletin, 203 . http://onlinepubs.trb.org/Onlinepubs/hrbbulletin/203/203-002.pdf

Wang, X., & Vom Hofe, R. (2020). Selected methods of planning analysis (2nd ed. 2020 edition). Springer. Springer Nature. https://doi.org/10.1007/978-981-15-2826-2

Whitney, V. (2019, September, 29). Activity & Trip Based Travel Models. Medium . https://medium.com/data-mining-the-city/activity-trip-based-travel-models-e4833571570

Cross-classification is a method for trip production estimation that disaggregates trip rates in an extended format for different categories of trips like home-based trips or non-home-based trips and different attributes of households such as car ownership or income.

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Network assignment

What is Network Assignment?

Role of Network Assignment in Travel Forecasting

Overview of Methods for Traffic Assignment for Highways

All-or-nothing Assignments

Incremental assignment

Brief History of Traffic Equilibrium Concepts

Calculating Generalized Costs from Delays

Challenges for Highway Traffic Assignment

Transit Assignment

Latest Developments

Page categories

Topic Circles

Trip Based Models

More pages in this category:

# what is network assignment.

In the metropolitan transportation planning and analysis, the network assignment specifically involves estimating travelers’ route choice behavior when travel destinations and mode of travel are known. Origin-destination travel demand are assigned to a transportation network in order to estimate traffic flows and network travel conditions such as travel time. These estimated outputs from network assignment are compared against observed data such as traffic counts for model validation .

Network assignment is a mathematical problem which is solved by a solution algorithm through the use of computer. It is usually resolved as a travel cost optimization problem for each origin-destination pair on a model network. For every origin-destination pair, a path is selected that typically minimizes travel costs. The simplest kind of travel cost is travel time from beginning to end of the trip. A more complex form of travel cost, called generalized cost, may include combinations of other costs of travel such as toll cost and auto operating cost on highway networks. Transit networks may include within generalized cost weights to emphasize out-of-vehicle time and penalties to represent onerous tasks. Usually, monetary costs of travel, such as tolls and fares, are converted to time equivalent based on an estimated value of time. The shortest path is found using a path finding algorithm .

The surface transportation network can include the auto network, bus network, passenger rail network, bicycle network, pedestrian network, freight rail network, and truck network. Traditionally, passenger modes are handled separately from vehicular modes. For example, trucks and passenger cars may be assigned to the same network, but bus riders often are assigned to a separate transit network, even though buses travel over roads. Computing traffic volume on any of these networks first requires estimating network specific origin-destination demand. In metropolitan transportation planning practice in the United States, the most common network assignments employed are automobile, truck, bus, and passenger rail. Bicycle, pedestrian, and freight rail network assignments are not as frequently practiced.

# Role of Network Assignment in Travel Forecasting

The urban travel forecasting process is analyzed within the context of four decision choices:

• Personal Daily Activity
• Locations to Perform those Activities
• Mode of Travel to Activity Locations, and
• Travel Route to the Activity Locations.

Usually, these four decision choices are named as Trip Generation , Trip Distribution , Mode Choice , and Traffic Assignment. There are variations in techniques on how these travel decision choices are modeled both in practice and in research. Generalized cost, which is typically in units of time and is an output of the path-choice step of the network assignment process, is the single most important travel input to other travel decision choices, such as where to travel and by which mode. Thus, the whole urban travel forecasting process relies heavily on network assignment. Generalized cost is also a major factor in predicting socio-demographic and spatial changes. To ensure consistency in generalized cost between all travel model components in a congested network, travel cost may be fed back to the earlier steps in the model chain. Such feedback is considered “best practice” for urban regional models. Outputs from network assignment are also inputs for estimating mobile source emissions as part of a review of metropolitan area transportation plans, a requirement under the Clean Air Act Amendments of 1990 for areas not in attainment of the National Ambient Air Quality Standard.

# Overview of Methods for Traffic Assignment for Highways

This topic deals principally with an overview of static traffic assignment. The dynamic traffic assignment is discussed elsewhere.

There are a large number of traffic assignment methods, but they all have at their core a procedure called “all-or-nothing” (AON) traffic assignment. All-or-nothing traffic assignment places all trips between an origin and destination on the shortest path between that origin and destination and no trips on any other possible path (compare path finding algorithm for a step-by-step introduction). Shortest paths may be determined by a well-known algorithm by Dijkstra; however, when there are turn penalties in the network a different algorithm, called Vine building , must be used instead.

# All-or-nothing Assignments

The simplest assignment algorithm is the all-or-nothing traffic assignment. In this algorithm, flows from every origin to every destination are assigned using the path finding algorithm , and travel time remains unchanged regardless of travel volumes.

All-or-nothing traffic assignment may be used when delays are unimportant for a network. Another alternative to the user-equilibrium technique is the stochastic traffic assignment technique, which assumes variation in link level travel time.

One of the earliest, computationally efficient stochastic traffic assignment algorithms was developed by Robert Dial. [1] More recently the k-shortest paths algorithm has gained popularity.

The biggest disadvantage of the all-or-nothing assignment and the stochastic assignment is that congestion cannot be considered. In uncongested networks, these algorithms are very useful. In congested conditions, however, these algorithm miss that some travelers would change routes to avoid congestion.

# Incremental assignment

The incremental assignment method is the simplest way to (somewhat rudimentary) consider congestion. In this method, a certain share of all trips (such as half of all trips) is assigned to the network. Then, travel times are recalculated using a volume-delay function , or VDF. Next, a smaller share (such as 25% of all trips) is assigned based using the revised travel times. Using the demand of 50% + 25%, travel times are recalculated again. Next, another smaller share of trips (such as 10% of all trips) is assigned using the latest travel times.

A large benefit of the incremental assignment is model runtime. Usually, flows are assigned within 5 to 10 iterations. Most user-equilibrium assignment methods (see below) require dozens of iterations, which increases the runtime proportionally.

In the incremental assignment, the first share of trips is assigned based on free-flow conditions. Following iterations see some congestion, on only the very last trip to be assigned will consider true congestion levels. This is reasonable for lightly congested networks, as a large number of travelers could travel at free-flow speed.

The incremental assignment works unsatisfactorily in heavily congested networks, as even 50% of the travel demand may lead to congestion on selected roads. The incremental assignment will miss the fact that a portion of the 50% is likely to select different routes.

# Brief History of Traffic Equilibrium Concepts

Traffic assignment theory today largely traces its origins to a single principle of “user equilibrium” by Wardrop [2] in 1952. Wardrop’s “first” principle simply states (slightly paraphrased) that at equilibrium not a single driver may change paths without incurring a greater travel impedance . That is, any used path between an origin and destination must have a shortest travel time between the origin and destination, and all other paths must have a greater travel impedance. There may be multiple paths between an origin and destination with the same shortest travel impedance, and all of these paths may be used.

Prior to the early 1970’s there were many algorithms that attempted to solve for Wardrop’s user equilibrium on large networks. All of these algorithms failed because they either did not converge properly or they were too slow computationally. The first algorithm to be able to consistently find a correct user equilibrium on a large traffic network was conceived by a research group at Northwestern University (LeBlanc, Morlok and Pierskalla) in 1973. [3] This algorithm was called “Frank-Wolfe decomposition” after the name of a more general optimization technique that was adapted, and it found the minimum of an “objective function” that came directly from theory attributed to Beckmann from 1956. [4] The Frank-Wolfe decomposition formulation was extended to the combined distribution/assignment problem by Evans in 1974. [5]

A lack of extensibility of these algorithms to more realistic traffic assignments prompted model developers to seek more general methods of traffic assignment. A major development of the 1980s was a realization that user equilibrium traffic assignment is a “variational inequality” and not a minimization problem. [6] An algorithm called the method of successive averages (MSA) has become a popular replacement for Frank-Wolfe decomposition because of MSA’s ability to handle very complicated relations between speed and volume and to handle the combined distribution/mode-split/assignment problem. The convergence properties of MSA were proven for elementary traffic assignments by Powell and Sheffi and in 1982. [7] MSA is known to be slower on elementary traffic assignment problems than Frank-Wolfe decomposition, although MSA can solve a wider range of traffic assignment formulations allowing for greater realism.

A number of enhancements to the overall theme of Wardop’s first principle have been implemented in various software packages. These enhancements include: faster algorithms for elementary traffic assignments, stochastic multiple paths, OD table spatial disaggregation and multiple vehicle classes.

# Calculating Generalized Costs from Delays

Equilibrium traffic assignment needs a method (or series of methods) for calculating impedances (which is another term for generalized costs) on all links (and nodes) of the network, considering how those links (and nodes) were loaded with traffic. Elementary traffic assignments rely on volume-delay functions (VDFs), such as the well-known “BPR curve” (see NCHRP Report 365), [8] that expressed travel time as a function of link volume and link capacity. The 1985 US Highway Capacity Manual (and later editions through 2010) made it clear to transportation planners that delays on large portions of urban networks occur mainly at intersections, which are nodes on a network, and that the delay on any given intersection approach relates to what is happening on all other approaches. VDFs are not suitable for situations where there is conflicting and opposing traffic that affects delays. Software for implementing trip-based models are now incorporating more sophisticated delay relationships from the Highway Capacity Manual and other sources, although many MPO forecasting models still use VDFs, exclusively.

# Challenges for Highway Traffic Assignment

Numerous practical and theoretical inadequacies pertaining to Static User Equilibrium network assignment technique are reported in the literature. Among them, most widely noted concerns and challenges are:

• Inadequate network convergence;
• Continued use of legacy slow convergent network algorithm, despite availability of faster solution methods and computers;
• Non-unique route flows and link flows for multi-class assignments and for assignment on networks that include delays from opposing and conflicting traffic;
• Continued use of VDFs , when superior delay estimation techniques are available;
• Unlikeness of a steady-state network condition;
• Impractical assumption that all drivers have flawless route information and are acting without bias;
• Every driver travels at the same congested speed, no vehicle traveling on the same link overtakes another vehicle;
• Oncoming traffic does not affect traffic flows;
• Interruptions, such as accidents or inclement weather, are not represented;
• Traffic does not form queues;
• Continued use of multi-hour time periods, when finer temporal detail gives better estimates of delay and path choice.

# Transit Assignment

Most transit network assignment in implementation is allocation of known transit network specific demand based on routes, vehicle frequency, stop location, transfer point location and running times. Transit assignments are not equilibrium, but can be either all-or-nothing or stochastic. Algorithms often use complicated expressions of generalized cost which include the different effects of waiting time, transfer time, walking time (for both access and egress), riding time and fare structures. Estimated transit travel time is not directly dependent on transit passenger volume on routes and at stations (unlike estimated highway travel times, which are dependent on vehicular volumes on roads and at intersection). The possibility of many choices available to riders, such as modes of access to transit and overlaps in services between transit lines for a portion of trip segments, add further complexity to these problems.

# Latest Developments

With the increased emphasis on assessment of travel demand management strategies in the US, there have been some notable increases in the implementation of disaggregated modeling of individual travel demand behavior. Similar efforts to simulate travel route choice on dynamic transportation network have been proposed, primarily to support the much needed realistic representation of time and duration of roadway congestion. Successful examples of a shift in the network assignment paradigm to include dynamic traffic assignment on a larger network have emerged in practice. Dynamic traffic assignments are able to follow UE principles. An even newer topic is the incorporation of travel time reliability into path building.

# References

Dial , Robert Barkley, Probabilistic Assignment; a Multipath Traffic Assignment Model Which Obviates Path Enumeration, Thesis (Ph.D.), University of Washington, 1971. ↩︎

Wardrop, J. C., Some Theoretical Aspects of Road Traffic Research, Proceedings, Institution of Civil Engineers Part 2, 9, pp. 325–378. 1952. ↩︎

LeBlanc, Larry J., Morlok, Edward K., Pierskalla, William P., An Efficient Approach to Solving the Road Network Equilibrium Traffic Assignment Problem, Transportation Research 9, 1975, 9, 309–318. ↩︎

(opens new window) ) ↩︎

Evans, Suzanne P., Derivation and Analysis of Some Models for Combining Trip Distribution and Assignment, Transportation Research, Vol 10, pp 37–57 1976. ↩︎

Dafermos, S.C., Traffic Equilibrium and Variational Inequalities, Transportation Science 14, 1980, pp. 42-54. ↩︎

Powell, Warren B. and Sheffi, Yosef, The Convergence of Equilibrium Algorithms with Predetermined Step Sizes, Transportation Science, February 1, 1982, pp. 45-55. ↩︎

(opens new window) ). ↩︎

← Mode choice Dynamic Traffic Assignment →

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3.4: Trip Generation

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• David Levinson et al.
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Trip Generation is the first step in the conventional four-step transportation forecasting process (followed by Destination Choice, Mode Choice, and Route Choice), widely used for forecasting travel demands. It predicts the number of trips originating in or destined for a particular traffic analysis zone.

Every trip has two ends, and we need to know where both of them are. The first part is determining how many trips originate in a zone and the second part is how many trips are destined for a zone. Because land use can be divided into two broad category (residential and non-residential) we have models that are household based and non-household based (e.g. a function of number of jobs or retail activity).

For the residential side of things, trip generation is thought of as a function of the social and economic attributes of households (households and housing units are very similar measures, but sometimes housing units have no households, and sometimes they contain multiple households, clearly housing units are easier to measure, and those are often used instead for models, it is important to be clear which assumption you are using).

At the level of the traffic analysis zone, the language is that of land uses "producing" or attracting trips, where by assumption trips are "produced" by households and "attracted" to non-households. Production and attractions differ from origins and destinations. Trips are produced by households even when they are returning home (that is, when the household is a destination). Again it is important to be clear what assumptions you are using.

People engage in activities, these activities are the "purpose" of the trip. Major activities are home, work, shop, school, eating out, socializing, recreating, and serving passengers (picking up and dropping off). There are numerous other activities that people engage on a less than daily or even weekly basis, such as going to the doctor, banking, etc. Often less frequent categories are dropped and lumped into the catchall "Other".

Every trip has two ends, an origin and a destination. Trips are categorized by purposes , the activity undertaken at a destination location.

Observed trip making from the Twin Cities (2000-2001) Travel Behavior Inventory by Gender

Some observations:

• Men and women behave differently on average, splitting responsibilities within households, and engaging in different activities,
• Most trips are not work trips, though work trips are important because of their peaked nature (and because they tend to be longer in both distance and travel time),
• The vast majority of trips are not people going to (or from) work.

People engage in activities in sequence, and may chain their trips. In the Figure below, the trip-maker is traveling from home to work to shop to eating out and then returning home.

Specifying Models

How do we predict how many trips will be generated by a zone? The number of trips originating from or destined to a purpose in a zone are described by trip rates (a cross-classification by age or demographics is often used) or equations. First, we need to identify what we think the relevant variables are.

The total number of trips leaving or returning to homes in a zone may be described as a function of:

\[T_h = f(housing \text{ }units, household \text{ }size, age, income, accessibility, vehicle \text{ }ownership)\]

Home-End Trips are sometimes functions of:

• Housing Units
• Household Size
• Accessibility
• Vehicle Ownership
• Other Home-Based Elements

At the work-end of work trips, the number of trips generated might be a function as below:

\[T_w=f(jobs(area \text{ }of \text{ } space \text{ } by \text{ } type, occupancy \text{ } rate\]

Work-End Trips are sometimes functions of:

• Area of Workspace
• Occupancy Rate
• Other Job-Related Elements

Similarly shopping trips depend on a number of factors:

\[T_s = f(number \text{ }of \text{ }retail \text{ }workers, type \text{ }of \text{ }retail, area, location, competition)\]

Shop-End Trips are sometimes functions of:

• Number of Retail Workers
• Type of Retail Available
• Area of Retail Available
• Competition
• Other Retail-Related Elements

A forecasting activity conducted by planners or economists, such as one based on the concept of economic base analysis, provides aggregate measures of population and activity growth. Land use forecasting distributes forecast changes in activities across traffic zones.

Estimating Models

Which is more accurate: the data or the average? The problem with averages (or aggregates) is that every individual’s trip-making pattern is different.

To estimate trip generation at the home end, a cross-classification model can be used. This is basically constructing a table where the rows and columns have different attributes, and each cell in the table shows a predicted number of trips, this is generally derived directly from data.

In the example cross-classification model: The dependent variable is trips per person. The independent variables are dwelling type (single or multiple family), household size (1, 2, 3, 4, or 5+ persons per household), and person age.

The figure below shows a typical example of how trips vary by age in both single-family and multi-family residence types.

The figure below shows a moving average.

Non-home-end

The trip generation rates for both “work” and “other” trip ends can be developed using Ordinary Least Squares (OLS) regression (a statistical technique for fitting curves to minimize the sum of squared errors (the difference between predicted and actual value) relating trips to employment by type and population characteristics.

The variables used in estimating trip rates for the work-end are Employment in Offices (\(E_{off}\)), Retail (\(E_{ret}\)), and Other (\(E_{oth}\))

A typical form of the equation can be expressed as:

\[T_{D,k}=a_1E_{off,k}+a_2E_{oth,k}+a_3E_{ret,k}\]

• \(T_{D,k}\) - Person trips attracted per worker in Zone k
• \(E_{off,i}\) - office employment in the ith zone
• \(E_{oth,i}\) - other employment in the ith zone
• \(E_{ret,i}\)- retail employment in the ith zone
• \(a_1,a_2,a_3\) - model coefficients

Normalization

For each trip purpose (e.g. home to work trips), the number of trips originating at home must equal the number of trips destined for work. Two distinct models may give two results. There are several techniques for dealing with this problem. One can either assume one model is correct and adjust the other, or split the difference.

It is necessary to ensure that the total number of trip origins equals the total number of trip destinations, since each trip interchange by definition must have two trip ends.

The rates developed for the home end are assumed to be most accurate,

The basic equation for normalization:

\[T'_{D,j}=T_{D,j} \dfrac{ \displaystyle \sum{i=1}^I T_{O,i}}{\displaystyle \sum{j=1}^J T_{TD,j}}\]

Sample Problems

Planners have estimated the following models for the AM Peak Hour

\(T_{O,i}=1.5*H_i\)

\(T_{D,j}=(1.5*E_{off,j})+(1*E_{oth,j})+(0.5*E_{ret,j})\)

\(T_{O,i}\) = Person Trips Originating in Zone \(i\)

\(T_{D,j}\) = Person Trips Destined for Zone \(j\)

\(H_i\) = Number of Households in Zone \(i\)

You are also given the following data

A. What are the number of person trips originating in and destined for each city?

B. Normalize the number of person trips so that the number of person trip origins = the number of person trip destinations. Assume the model for person trip origins is more accurate.

Solution to Trip Generation Problem Part A

\[T'_{D,j}=T_{D,j} \dfrac{ \displaystyle \sum{i=1}^I T_{O,i}}{\displaystyle \sum{j=1}^J T_{TD,j}}=>T_{D,j} \dfrac{37500}{36750}=T_{D,j}*1.0204\]

Solution to Trip Generation Problem Part B

Modelers have estimated that the number of trips leaving Rivertown (\(T_O\)) is a function of the number of households (H) and the number of jobs (J), and the number of trips arriving in Marcytown (\(T_D\)) is also a function of the number of households and number of jobs.

\(T_O=1H+0.1J;R^2=0.9\)

\(T_D=0.1H+1J;R^2=0.5\)

Assuming all trips originate in Rivertown and are destined for Marcytown and:

Rivertown: 30000 H, 5000 J

Marcytown: 6000 H, 29000 J

Determine the number of trips originating in Rivertown and the number destined for Marcytown according to the model.

Which number of origins or destinations is more accurate? Why?

T_Rivertown =T_O ; T_O= 1(30000) + 0.1(5000) = 30500 trips

T_(MarcyTown)=T_D ; T_D= 0.1(6000) + 1(29000) = 29600 trips

Origins(T_{Rivertown}) because of the goodness of fit measure of the Statistical model (R^2=0.9).

Modelers have estimated that in the AM peak hour, the number of trip origins (T_O) is a function of the number of households (H) and the number of jobs (J), and the number of trip destinations (T_D) is also a function of the number of households and number of jobs.

\(T_O=1.0H+0.1J;R^2=0.9\)

Suburbia: 30000 H, 5000 J

Urbia: 6000 H, 29000 J

1) Determine the number of trips originating in and destined for Suburbia and for Urbia according to the model.

2) Does this result make sense? Normalize the result to improve its accuracy and sensibility?

• \(T_{O,i}\) - Person trips originating in Zone i
• \(T_{D,j}\) - Person Trips destined for Zone j
• \(T_{O,i'}\) - Normalized Person trips originating in Zone i
• \(T_{D,j'}\) - Normalized Person Trips destined for Zone j
• \(T_h\) - Person trips generated at home end (typically morning origins, afternoon destinations)
• \(T_w\) - Person trips generated at work end (typically afternoon origins, morning destinations)
• \(T_s\) - Person trips generated at shop end
• \(H_i\) - Number of Households in Zone i
• \(E_{off,k}\) - office employment in Zone k
• \(E_{ret,k}\) - retail employment in Zone k
• \(E_{oth,k}\) - other employment in Zone k
• \(B_n\) - model coefficients

Abbreviations

• H2W - Home to work
• W2H - Work to home
• W2O - Work to other
• O2W - Other to work
• H2O - Home to other
• O2H - Other to home
• O2O - Other to other
• HBO - Home based other (includes H2O, O2H)
• HBW - Home based work (H2W, W2H)
• NHB - Non-home based (O2W, W2O, O2O)

External Exercises

Use the ADAM software at the STREET website and try Assignment #1 to learn how changes in analysis zone characteristics generate additional trips on the network.

Additional Problems

• the start and end time (to the nearest minute)
• start and end location of each trip,
• primary mode you took (drive alone, car driver with passenger, car passenger, bus, LRT, walk, bike, motorcycle, taxi, Zipcar, other). (use the codes provided)
• purpose (to work, return home, work related business, shopping, family/personal business, school, church, medical/dental, vacation, visit friends or relatives, other social recreational, other) (use the codes provided)
• if you traveled with anyone else, and if so whether they lived in your household or not.

Bonus: Email your professor at the end of everyday with a detailed log of your travel diary. (+5 points on the first exam)

• Are number of destinations always less than origins?
• Pose 5 hypotheses about factors that affect work, non-work trips? How do these factors affect accuracy, and thus normalization?
• What is the acceptable level of error?
• Describe one variable used in trip generation and how it affects the model.
• What is the basic equation for normalization?
• Which of these models (home-end, work-end) are assumed to be more accurate? Why is it important to normalize trip generation models
• What are the different trip purposes/types trip generation?
• Why is it difficult to know who is traveling when?
• What share of trips during peak afternoon peak periods are work to home (>50%, <50%?), why?
• What does ORIO abbreviate?
• What types of employees (ORIO) are more likely to travel from work to home in the evening peak
• What does the trip rate tell us about various parts of the population?
• What does the “T-statistic” value tell us about the trip rate estimation?
• Why might afternoon work to home trips be more or less than morning home to work trips? Why might the percent of trips be different?
• Define frequency.
• Why do individuals > 65 years of age make fewer work to home trips?
• Solve the following problem. You have the following trip generation model:

\[Trips=B_1Off+B_2Ind+B_3Ret\]

And you are given the following coefficients derived from a regression model.

If there are 600 office employees, 300 industrial employees, and 200 retail employees, how many trips are going from work to home?

International Conference on Combinatorial Optimization and Applications

COCOA 2020: Combinatorial Optimization and Applications pp 681–696 Cite as

Trip-Vehicle Assignment Algorithms for Ride-Sharing

• Songhua Li 10 ,
• Minming Li 10 &
• Victor C. S. Lee 10  
• Conference paper
• First Online: 04 December 2020

832 Accesses

1 Citations

Part of the book series: Lecture Notes in Computer Science ((LNTCS,volume 12577))

The trip-vehicle assignment problem is a central issue in most peer-to-peer ride-sharing systems. Given a set of n available vehicles with respective locations and a set of m trip requests with respective origins and destinations, the objective is to assign requests to vehicles with the minimum overall cost (which is the sum of the moving distances of the vehicles). Since the assignment constraints are well captured by edges matched in graphs, we investigate the problem from a matching algorithm point of view. Suppose there are at most two requests sharing a vehicle at any time, we answer an open question by Bei and Zhang (AAAI, 2018), that asks for a constant-approximation algorithm for the setting where the number ( m ) of requests is no more than twice the number ( n ) of vehicles, i.e., \(m\le 2n\) . We propose an \(O(n^{4})\) -time 2.5-approximation algorithm, which is built upon a solution of the M inimum-weight F ixed-size M atching problem with unmatched vertex P enalty (MFMP), in which the cost is the sum of the weights of both matched edges and unmatched vertices. Then, we study a more general setting that also allows \(m> 2n\) . We propose a dynamic assignment algorithm that is built upon a solution of the M inimum W eight M atching problem with unmatched vertex P enalty (MWMP). Further, we extend the dynamic assignment algorithm to an online setting where on-demand trip requests appear over time. Experiments are conducted on a real-world data set of trip records showing that our algorithms actually achieve good performances.

• Ride-sharing system
• Trip-vehicle assignment
• Matching algorithm

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Purchases are for personal use only

Note that our implementation data in Sect.  5 does not necessarily follow these properties.

For ease of analysis, our model admits that every pair of requests can be grouped together to share a vehicle, which is also an assumption in [ 5 ].

This number is represented by i in Algorithm 1.

This tackles the hurdle ( a ) as presented in Sect.  1 .

In either DPAA or DPAA \(_D\) , the matching loop refers to lines 7–11 of the pseudo code.

In the online setting where trip requests are released over time, we do not consider the service deadline of the requests and only aim to service all the released requests with the overall moving distance of the vehicles minimized.

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Acknowledgements

Part of this work was done when Songhua Li was visiting the Singapore University of Technology and Design. Minming Li is also from City University of Hong Kong Shenzhen Research Institute, Shenzhen, P.R. China. The work described in this paper was partially supported by Project 11771365 supported by NSFC. We would like to thank Kaiyi Liao for his help in the implementation of our algorithms and we also thank all the anonymous reviewers for their comments.

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Li, S., Li, M., Lee, V.C.S. (2020). Trip-Vehicle Assignment Algorithms for Ride-Sharing. In: Wu, W., Zhang, Z. (eds) Combinatorial Optimization and Applications. COCOA 2020. Lecture Notes in Computer Science(), vol 12577. Springer, Cham. https://doi.org/10.1007/978-3-030-64843-5_46

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UNCLASSIFIED (U)

OFFICIAL TRAVEL

(CT:LOG-343;   02-11-2022) (Office of Origin:  A/LM)

14 FAM 531  EmploymenT and Assignment Travel

(CT:LOG-343;   02-11-2022) (State/USAGM/USAID/Commerce/Agriculture)

When two or more types of travel are combined, the pertinent provisions apply separately to each segment of the trip.  Types of official travel follow below.

14 FAM 531.1  Appointment Travel

a. Official travel and transportation for U.S. citizen employees, their families, and effects, may be authorized from place or places of residence or other place specifically authorized to official duty station.

b. Effects may be authorized to be shipped at U.S. Government expense from place of storage.  Shipment of effects is authorized for employees whose tour of duty at post is one year or more or who serve less than a year and are transferred or otherwise removed from post for the convenience of the U.S. Government (see 3 FAM 2440 regarding curtailments).

14 FAM 531.2  Alternate-Seat-of-Government Travel

a. Official travel and transportation for U.S. citizen employees, their families, and effects, may be authorized to and from the alternate seat of government.

b. There is no per diem at destination unless specifically authorized. Shipment and storage of effects, and privately owned vehicle, may be authorized.

14 FAM 531.3  Relocation Travel

Official travel and transportation may be authorized for employees to move from one official duty station to another.  This includes permanent change-of-station (PCS) and transfer moves.

14 FAM 531.4  Home Leave Travel

a. Official travel and transportation may be authorized for U.S. citizen employees and their families from post or any place abroad where presence is due to U.S. Government orders to home leave address within the United States (or U.S. commonwealth or possessions) and return to post of assignment or a new official duty station.  Home leave travel is not authorized for family members already on separate maintenance allowance (SMA) authorization (see also 14 FAM 536.1 ).

b. Employees and their families traveling should spend 20 workdays in the United States (see 3 FAM 3434.2 for exceptions).  Except as provided in 14 FAM 532.4 the family may not travel until the employee is eligible for home leave and has been issued home leave orders.

14 FAM 531.5  Rest and Recuperation Travel

a. Travel of an employee and eligible family members may be authorized and performed in accordance with 14 FAM 523.2-1 , subparagraph f(1)(d) and in 3 FAM 3720 .

b. Each post eligible for rest and recuperation (R&R) travel will fund one of the following three travel options to employees and eligible family members:

(1) Round-trip travel to post's designated foreign relief point.  Lists of eligible posts by regional area and their designated relief points are in 3 FAH-1 Exhibit H-3722(1) through 3 FAH-1 Exhibit H-3722(5) ; or

(2)  Round-trip travel to any one city in the United States (the 50 States and the District of Columbia) or one city in its territories including American Samoa, the Commonwealth of Puerto Rico, Guam, the Commonwealth of the Northern Mariana Islands, and the U.S. Virgin Islands; or

c.  Only the designated foreign relief point, the traveler's selected city in the United States or U.S. territory, or "R&R Cost-Construct Cap" can be shown as the destination on the authorized itinerary of the R&R travel authorization.

e.  Employees authorized premium class travel through MED/DRAD will have a cost-construct cap established on a case-by-case basis using the same methodology used for economy caps outlined in 3 FAH-1 H-3726.3 .

f.  The Department recommends that posts use the lowest cost unrestricted airfares for travel to the designated relief point or U.S. city or U.S territory.  However, funding for R&R travel is a post function and, as such, the final decision whether to use restricted or unrestricted fares for R&R travel is a post responsibility.

14 FAM 531.6  Marine Security Guard

See 12 FAM 435 .

14 FAM 531.7  Military Furlough, Resignation, Retirement, and Other Separation Travel

a. Official travel and transportation may be authorized for U.S. citizen employees, their eligible family members, and effects, from post or any place where presence is due to U.S. Government orders to designated place of residence in the United States (see definition of "United States" in 14 FAM 511.3 ).

b. When a U.S. citizen employee elects to reside at other than the designated place of residence, expenses must be allowed based on constructive cost (for "cost constructed travel," see 14 FAM 511.3 and 14 FAM 612.3 ) to designated place of residence in the United States.  See 3 FAM 2510 on separation of U.S. citizen employees and 3 FAM 2560 on military furlough.

c.  This regulation provides Civil Service employees, who mandatorily converted to Civil Service from Foreign Service under the Foreign Service Act of 1980, those benefits of travel and/or transportation of effects to which they were entitled at the time of such mandatory conversion.

14 FAM 532  Family tRAVEL

14 FAM 532.1  Family Travel for Representational Purposes

14 FAM 532.1-1  Eligibility and Purpose

Travel for representational purposes may be authorized for one family member only.  The authorizing officer is expected to make sparing and judicious use of this authorization.  In all cases, the justification must demonstrate a clear advantage to the United States.

14 FAM 532.1-2  Within Country of Assignment

a. As a general guideline, local travel of a family member should be authorized when:

(1)  Representation by the officer alone could not be accomplished effectively; or

(2)  Protocol or local customs would be served; or

(3)  The travel is necessary in connection with VIP visits or important meetings at which spouses of foreign dignitaries are present.

b. The chief of mission in consultation with heads of other agencies in their country of assignment will develop local rules and practices to promote the maximum degree of uniformity in the exercise of this authority.

14 FAM 532.1-3  Outside Country of Assignment

Representational travel outside the country of assignment is restricted to family members of high-level officers and will be authorized only when a clear need for dual representation exists.  Normally, travel will be restricted to eligible family members of chiefs of mission, deputy chiefs of mission, country public affairs officers, and USAID mission directors or USAID representatives.  However, in exceptional circumstances, the eligible family members of a subordinate officer may be authorized such travel.  Typical of the circumstances warranting representational travel outside the country are the following:

(1)  When an ambassador or USAID mission director accompanies a foreign dignitary to the United States on a state visit or as a presidential guest and the dignitary is accompanied by a spouse or other members of the household;

(2)  When a State, or USAID officer attends an international conference or meeting sponsored by a group or organization of nations, such as the United Nations, and the spouses of participants have also been invited to attend; and

(3)  When the President sends U.S. delegations abroad or congressional or other high-level delegations proceed abroad, accompanied by their spouses.

14 FAM 532.1-4  Domestic-Based Employees

Representational travel by family members of domestically assigned employees is restricted to the Secretary, Deputy Secretary, Deputy Secretary for Management and Resources, and Under Secretaries, unless a waiver is granted by M, and will be authorized only when a clear need for such representation exists.

14 FAM 532.1-5  Authorization and Documentation

a. Department of State : The chief of mission may (subject to the availability of travel funds) authorize representational travel within and/or outside the country of assignment for employees at post.  This authority may be redelegated only to the deputy chief of mission.  The Assistant Secretary of the regional bureau may authorize for the chief of mission.  For representational travel outside the country of assignment, advance approval must also be obtained from the assistant secretary of the regional bureau.  For domestic based employees, the Under Secretary for Management must approve all representational travel for family members.  Representational travel by a family member of M must be approved by D.

b. USAID :  The director of the USAID mission or USAID representative may (subject to the availability of travel funds) authorize representational travel within and/or outside the country of assignment.  This authority may not be redelegated. For representational travel outside the country of assignment, advance approval must also be obtained from the regional bureau Assistant Administrator in Washington.

c. The officials cited above must provide and sign a justification statement.  For control and inspection purposes, the authorizing officer should record and file the justification statement in the Department's eTravel Services (ETS) software (currently E2 Solutions).

14 FAM 532.2  Adding New Eligible Family Members

Employees who wish to add a new eligible family member – EFM - (see 14 FAM 511.3 for the definition of "eligible family member") do so by completing Form OF-126, Foreign Service Residency and Dependent Report, to GTM/EX/IDSD or HCTM/FSC for USAID staff.  Once the new EFM is added to the Form OF-126 then the employee’s travel authorization will be updated to include new EFM and travel expenses may be incurred based on the updated travel authorization, notwithstanding the time limitation specified in 14 FAM 584.2 .  Travel will be authorized from either the location at which the new EFM joined the family (for example, place of birth or adoption) or from the employee’s official home of record.  Shipment and storage of additional effects may be authorized in accordance with 14 FAM 613.2 .

14 FAM 532.3  Advance Return of Family Financed by U.S. Government

14 FAM 532.3-1  General Policy

In certain cases, an employee's family may be authorized, before the employee's eligibility for travel, to return to employee's residence in the United States.

14 FAM 532.3-2  Conditions of Authorization

a. The Department of State, USAGM, Commerce, Agriculture, or the USAID mission director or USAID representative may authorize advance travel of an employee's family members when the chief of mission or the head of the agency establishment abroad determines that the public interest requires the return of a member of the family for compelling personal reasons of a humanitarian or compassionate nature, including but not limited to cases which may involve physical or mental health or death of any member of the immediate family.

b. The Department or Agency in Washington, DC, may authorize advance travel of family members when there is an obligation imposed by an authority or circumstances over which the individual has no control.  Advance travel may be authorized by the Department or Agency in Washington, DC, after family members have been at the post at least 6 months under the following conditions:

(1)  A child who is not eligible for educational travel (see 14 FAM 532.5 ) has been at a post abroad and educational needs (for the equivalent of grades 1 through 8 only) so require; or

(2)  A child 21 years or older, is unmarried, and has traveled to the post before attaining such age (see 14 FAM 532.6 ).

14 FAM 532.3-3  Authorized Costs

Only one-way transportation will be authorized for advance return of family.  If a family member subsequently travels at U.S. Government expense to the same or another post to which the employee is assigned, the total cost of the advance return and subsequent travel may not exceed the cost which would have been incurred had the family member traveled at the same time as the employee.

14 FAM 532.3-4  Repayment Agreement

Before any obligation of U.S. Government funds is incurred, the employee must execute a repayment agreement in accordance with the format in Form DS-4020, Repayment Agreement for Advance Travel of Family.  The original and one copy should be forwarded to:

(1)  State :  GTM/CDA, by memorandum, subject:  APER;

(2)  USAID :  M/PM, USAID/W as an attachment to a memorandum;

(3)  Commerce : USFCS/OIO/OFSP as an attachment to a memorandum;

(4)  USAGM :  E/O, P/N, VOA/X, and D/OHR as an attachment to a memorandum.

(5)  USDA/FAS :  Foreign Agricultural Affairs, International Services Division; and

(6)  APHIS :  International Services/Administrative Services/Personnel.

14 FAM 532.3-5  Repayment Requirements

The conditions under which repayment must be made by the employee for travel expenses borne by the U.S. Government in connection with the advance return of employee's family are as follows:

(1)  The employee fails to complete the service period (see 3 FAH-1 H-2423 , subparagraph c) required to become eligible for travel and transportation at U.S. Government expense; or

(2)  There is a change of dependency status which cancels the eligibility of family member(s) for return travel to the United States (see definition in 14 FAM 511.3 ) at U.S. Government expense.  (A divorce or an annulment prior to the issuance of travel orders no longer cancels eligibility of family members for return travel to the United States.)

14 FAM 532.3-6  Repayment Liquidation or Refund

(CT:LOG-343;   02-11-2022) (State/USAGM/USAID/Commerce/Agriculture)

If the employee is subsequently transferred, assigned, separated, or returned on leave at U.S. Government expense to the United States and the expenses of the advance travel become a proper obligation of the U.S. Government, the employee will be relieved of the obligation set forth in the repayment agreements to the amount of allowable expenses (see 14 FAM 532.3-4 ).  If the employee has previously made repayment, employee may request and receive an appropriate refund.

14 FAM 532.4  Advance Travel of Family Financed by the Employee

a. The employee may arrange for advance travel of family, paying the cost initially and claiming reimbursement after the employee has been issued travel authorization which covers the travel of family and after the employee has reached eligibility date.  Reimbursement is limited to the amounts payable had the family traveled at the same time as the employee.

b. Reimbursement may be made for advance travel or return travel to the United States for a spouse or domestic partner as defined in 3FAM 1610 and/or minor children of an employee who have traveled to the post as eligible family members even if, because of divorce, annulment or dissolution of domestic partnership, such spouse or domestic partner as defined in 3 FAM 1610 and/or minor children have ceased to be eligible family members as of the date the employee becomes eligible for travel.  Reimbursable travel may not be deferred more than 6 months after the employee completes personal travel pursuant to the authorization.

c.  If the advance travel of family was to the employee's temporary duty (TDY) post and the employee was transferred to the post at the end of the employee's TDY, employee may claim reimbursement for expenses of allowable travel and transportation of family and effects which were incurred prior to the effective date of transfer of the employee and the date of employee's transfer travel authorization.

14 FAM 532.5  Educational Travel

a. Travel of a child may be authorized in lieu of an educational allowance, once each way annually between school and the employee's post for secondary education and for college education in accordance with section 280, Standardized Regulations (Government Civilians, Foreign Areas) and the Federal Travel Regulations.

b. Unaccompanied air baggage is allowable in accordance with 14 FAM 613.3-1 .

14 FAM 532.6  Travel of Children 21 Years of Age or Older

a. An employee's child who is unmarried and who is 21 years of age or older may be authorized return travel to the employee's place of residence for separation purposes in the United States (see definition in 14 FAM 511.3 ), provided the child, when attaining the age of 21 was at, or proceeding to, a post abroad to which the employee was assigned.  The first travel authorization that is issued to the employee authorizing travel of the family after a child has reached the age of 21, constitutes authority for such travel.  The return of the child to the United States should be completed within 1 year of the date the employee's travel begins.

b. A child 21 years or older, who proceeds to the employee's post, may not be returned to the United States nor perform any travel at U.S. Government expense, except as provided for educational travel up to the 23rd birthday, plus additional years allowed for any military service, in subchapter 280 of the Standardized Regulations (Government Civilians, Foreign Areas).

c.  Travel of a child who is under 21 will usually be authorized to an employee's next assignment if the employee's transfer is to occur before the child's 21st birthday.  If that child's travel does not commence prior to turning 21, that authorization is no longer valid.

d. If a child commences R&R or home leave/return travel before attaining the age of 21 and turns 21 while in travel status, the child is authorized return to post under the travel authorization that was in effect prior to his turning 21.

14 FAM 532.7  Travel of Family While Employee Is on Temporary Duty (TDY) En Route to or from Post of Assignment

a. Payment of per diem during an employee's period of TDY, which may not exceed 30 calendar days total, is authorized for members of an employee's family accompanying the employee to the post of assignment only under the following conditions:

(1)  When the employee is ordered to stop within the country of destination for orientation, training, or consultation while en route to post of assignment;

(2)  When the employee is ordered to stopover outside the country of destination for orientation, training, or other TDY while en route to the post of assignment, provided that the stopover is in the positive interest of the U.S. Government and is made necessary by a threat to the health, safety, or well-being of the employee’s family if required to continue on to post of assignment other than in the company of the employee;

(3)  In cases where the family member, because of representative responsibility in the U.S. Government's interest, is required to stop at agency headquarters while en route abroad to employee's post of assignment in order to undergo special orientation and/or training designed to ensure the effective discharge of those responsibilities; or

(4)  In any other cases when specifically authorized by the agency in advance in writing in travel orders.

b. When an employee is ordered to stop for TDY in the United States or abroad en route to or from employee's post of assignment, the family does not have to accompany the employee as long as they join the employee at the stopover point.  Per diem at the stopover point may be allowed for members of the family only during the period of TDY of the employee and for the actual time at the TDY location.

c.  Per diem, not to exceed 3 work days, may be authorized when an employee or the employee's family members who are at a constituent post and are traveling on home leave, transfer, or separation orders must stop, at the time of travel, at the Embassy in country or at an embassy in a neighboring country for the purpose of storing or retrieving effects or obtaining passports, visas, or immunizations.

d. Stopovers should generally not be authorized for family members in connection with international, interagency, interregional, or intermission conferences, unless specifically authorized by the agency in advance in writing and reflected in travel orders.

14 FAM 532.8  Return Travel of Spouse, Domestic Partner as Defined in 3 FAM 1610, and/or Dependent Children to the United States in Connection with Marital Separation, or Divorce, or Statement of Dissolution of Domestic Partnership

a. Return travel of an employee's spouse or domestic partner as defined in 3 FAM 1610 may be authorized to the employee's service separation address in the United States (see definition of "United States" in 14 FAM 511.3 ) or any other location on a cost-constructive basis from the employee's post of origin to the employee's separation address when a permanent marital separation or divorce is intended, or a statement of dissolution of domestic partnership has been submitted.  Generally, a separation agreement should exist, but in the absence of an agreement, the chief of mission or head of agency's establishment abroad may determine that such travel is warranted and may initiate authorization action.  The circumstances upon which this determination is based should be summarized in writing and retained at post in accordance with 5 FAH-4, Records Management Handbook.

b. Return travel of spouse or domestic partner as defined in 3 FAM 1610 may be included in the first travel authorization issued to the employee authorizing travel of the family after an agreement to separate, divorce, or dissolve a domestic partnership is reached.  In the circumstances referred to in paragraph a of this section, such travel may also be requested as advance travel in accordance with 14 FAM 532.3 and 14 FAM 532.4 .

c.  Only one-way transportation to the employee's service separation address, or to any other location in the United States on a cost-constructive basis from the employee's post of origin to his or her separation address, will be authorized for return travel of spouse or domestic partner as defined in 3 FAM 1610 .  If the employee subsequently requests travel of the spouse at U.S. Government expense to the same or another post to which the employee is assigned, the total cost of the return and subsequent travel may not exceed the cost which would have been incurred had the spouse or domestic partner as defined in 3 FAM 1610 traveled at the same time as the employee.  In such cases, if the cost of the return and subsequent travel exceeds the employee's authorized travel, the employee will be liable for payment of the excess cost.

d. Before any expenses are incurred for return travel of spouse or domestic partner as defined in 3 FAM 1610 , the spouse or domestic partner as defined in 3 FAM 1610 must execute an agreement in accordance with the format in Form DS-4021, Agreement for Return Travel of Spouse (or domestic partner).  This agreement states that the spouse or domestic partner as defined in 3 FAM 1610 understands that travel back to the same post will not be authorized at U.S. Government expense, and that the agreement is signed voluntarily.

e. Travel of dependent children of an employee may be authorized under this provision only if a legal custody agreement exists or the employee otherwise agrees in writing to permit the children to leave post permanently with the spouse.  The employee must also submit a revised Form OF-126, Foreign Service Residence and Dependency Report, to declare as a loss those children for whom return travel is requested under this provision (see 3 FAH-1 H-2347.8 , subparagraph a).  The employee may also request advance travel of children in accordance with 14 FAM 532.3 , if travel is not intended to be a permanent return to the United States.

14 FAM 532.9  Transfer Travel

(CT:LOG-343;   02-11-2022) (State/USAGM/USAID/Commerce/Agriculture) (Foreign Service)

a. Official travel and transportation may be authorized for U.S. citizen and Foreign Service national employees, their families and effects, from old post, or any place where presence is due to U.S. Government orders, to new post.  Transportation of effects is allowed from old post to new post and/or to point of storage; or to new post from old post, previous posts, and/or points of authorized storage.

b. Effects may be shipped between places other than those authorized subject to provisions in 14 FAM 612.3 .  When emergency conditions exist at the new post, another destination may be designated for travel of the family and transportation and storage of effects and a motor vehicle.  Upon termination of the emergency, travel and transportation to the new post may be authorized.

14 FAM 532.10  Spouse Travel to Obtain a Visa or Reset Residency

Management officials at post may authorize, from post funds, travel expenses when the spouse of an employee assigned to post must travel out of country to obtain appropriate visas or reset residency permissions to remain in-country when the host government will not accredit the spouse.  The travel expenses under this provision may include transportation expenses, per diem, and authorized miscellaneous expenses (e.g., visa fees, where authorized under 14 FAM 562.1 , subparagraphs a(1) through a(4).  Expenses incurred are for the spouse only.  Time in travel status should be minimized to the extent possible to obtain a visa or reset residency permissions at the most cost-effective point to post.  Spouses who are employed on family member appointments (FMA) or personal services agreements (PSA) are not authorized administrative leave for the purpose of the travel.

14 FAM 533  Temporary Duty (tdy) Travel

14 FAM 533.1  General

Official travel and transportation may be authorized for U.S. citizen employees from any place to TDY station or stations and thence to such place or to post (see also 14 FAM 532.7 covering travel of eligible family members). Official travel and transportation may be authorized for Locally Employed (LE) Staff from their post of employment to TDY station or stations and for return to the post of employment.

14 FAM 533.2  Authorizing Temporary Duty (TDY) Travel

a. State only :  Form JF-144, Temporary Duty (TDY) Official Travel Authorization, is used for approving TDY travel.  Approval may cover travel performed for administrative or medical purposes, rest and recuperation, short-term training, attendance at conferences, etc., between the United States and other countries, within the United States, or abroad.  Authorizations issued in the form of telegrams, etc., are confirmed by the subsequent issuance of a Form JF-144, or equivalent official form.

b. USAID only :  See ADS 522, Performance of Temporary Duty travel in the United States and Abroad.

c.  Commerce only :  Form CD-29, Travel Order, is used for authorizing TDY travel when headquarters, Washington, DC, issues the travel orders.  Otherwise, Form JF-144 is used when post issues the travel orders.  Included is travel for administrative purposes, rest and recuperation travel, short-term training, medical purposes, attendance at conferences, etc., performed abroad, within the United States, and between the United States and points abroad.  Authorizations issued in the form of telegrams are confirmed by the subsequent issuance of either a Form CD-29 or a Form JF-144.

d. USDA only :  Form AD-202, Travel Authorization, is used for authorizing TDY travel.

e. USAGM only :  Form IA-34-A is used for authorizing TDY travel; Form JF-144 is used for overseas correspondence travel.

14 FAM 533.3  Training Attendance

Official travel may be authorized for employees to receive training.

14 FAM 533.4  Conference Travel

14 FAM 533.4-1  Attendance

Agencies must select conference sites that minimize conference costs and conference attendees' travel costs.  Agencies must minimize conference attendees' travel costs by authorizing the minimum participation necessary to accomplish agency goals.  The authorizing official must assure that the number of attendees from the Department is necessary and justified.  In addition, the need for conference and meetings for which the total travel and per diem estimate exceeds $5,000 must be authorized by an Assistant Secretary, executive director, or equivalent.

14 FAM 533.4-2  Conference Site

When available, use U.S. Government-owned or U.S. Government-provided conference facilities to the maximum extent possible.  The authorizing officer should avoid conference sites that might appear extravagant to the public.

14 FAM 533.4-3  Conference Site Selection Process

a. Locality selection procedures :

(1)  When arranging to conduct a conference, the authorizing officer must consider at a minimum three alternative conference sites;

(2)  Each considered site must be selected based on the belief that it would result in lower overall conference costs and conference attendees' travel costs.  The sponsoring or co-sponsoring office must survey the cost of conference facilities at each of the considered sites, and must determine the potential cost to the U.S. Government of conducting the conference at each of the alternative sites.

b. Exception :  A conference site may be selected without following the procedures outlined above for the reason of disproportionate participation.  The procedures outlined above do not apply when a majority of the U.S. Government attendees are from the locality proposed as the conference site, or when only one site accomplishes conference goals.  In the latter case, the authorizing officer must certify in writing that the selected locality is the only conference site compatible with accomplishing the sponsoring or co-sponsoring office's objectives.

c.  Documentation :  The authorizing officer must document the cost of each alternative conference site, and must retain a record of the documentation for every conference held.  The authorizing officer must also make the documentation available for inspection by the Office of Inspector General (OIG), or for other interested parties.

14 FAM 533.5  Experts and Consultants Travel

Persons employed intermittently as consultants or experts and persons serving without compensation (including citizens or subjects of other countries) are authorized travel expenses, including per diem, while away from their homes or regular places of business, in accordance with 14 FAM 560 .

14 FAM 533.6  Information Meeting Travel

(CT:LOG-343;   02-11-2022) (State/USAGM/USAID/Commerce/Agriculture) (Foreign Service and Civil Service)

Official travel and transportation may be authorized for employees to attend a meeting to discuss general agency operations, and/or to review status reports or discussion topics of general interest.  If a site visit is conducted as part of the same trip, the entire trip should be considered a site visit (see 14 FAM 533.10 ).

14 FAM 533.7  International Conferences

When travel to, or in connection with, conferences is financed under Department of State appropriations available for international conferences, such travel must be performed in accordance with the provisions of the travel authorization and other appropriate instructions issued by the Department pertaining to the conference.

14 FAM 533.8  Invitational Travel Authorizations Federally Financed

Each invitational travel authorization must specify the purpose of the travel (e.g., conference attendance, information meeting, speech presentation, etc).

14 FAM 533.9  Invitational Travel Authorizations Non-Federally Financed

To defray the cost of air travel, any donations from non-Federal sources must comply with the Department's regulations in accommodations on airplanes ( 14 FAM 567.2 ), including all applicable OMB guidelines (OMB 93-11), as well as the Department’s regulations regarding gifts of invitational travel (see 2 FAM 962.12 ).

14 FAM 533.10  Site Travel

Travel of an employee may be authorized to visit a particular site in order to perform operational or managerial activities; e.g., oversee programs, grant operations, or management activities for internal control purposes; carry out an audit, inspection or repair activity; conduct negotiations; provide instructions; or provide technical assistance.

14 FAM 533.11  Special Mission Travel

Travel of an employee may be authorized to carry out a special agency mission such as involvement in noncombat military unit movements; providing security to a person or a shipment (e.g., diplomatic pouch); moving witnesses from residence to other locations; and covering travel by Federal beneficiaries and other nonemployees.

14 FAM 533.12  Speech or Presentation Travel

Travel of an employee may be authorized to make a speech or a presentation, deliver a paper, or otherwise take part in a formal program other than a training course where the authorizing official makes a specific determination in writing that such activity is related to and in furtherance of the agency’s mission.

14 FAM 534  Medical Travel

a. Official travel and transportation may be authorized for U.S. citizen employees and their eligible family members from any place where presence is due to U.S. Government orders to nearest locality where suitable medical care can be obtained and thence to an official duty station.

b. Travel of attendants may be authorized.  For other special provisions, see 16 FAM 316 and 14 FAM 523.2-1 , paragraph e.

14 fam 535  oTHER TRAVEL

14 FAM 535.1  Directed Departure

14 FAM 535.1-1  General

When, in accordance with 3 FAM 2443 , it is the judgment of a chief of a diplomatic mission that the departure of an employee assigned by the Department or Agency to a post under the chief of mission's jurisdiction would be in the interest of the U.S. Government, the authorizing officer at the post may issue a travel authorization detailing the employee to a nearby country.  For the Department, the post-authorizing officer may issue a travel authorization transferring a State Department employee and that employee's eligible family members to Washington, DC.  For USAID, a travel authorization transferring an employee to Washington, DC, must originate in or have prior approval of Washington, DC headquarters.  For USAGM, a travel authorization transferring an employee to Washington, DC must originate in or have prior approval of Washington, DC headquarters.

14 FAM 535.1-2  Procedures in Connection with Directed Departure

To authorize purchase of transportation permitting the detail of an employee or to transfer an employee and eligible family members in accordance with 3 FAM 2443 , chiefs of mission may allow issuance of Forms OF-1169, U.S. Government Transportation Request (GTRs).  The travel order establishing the official obligation of funds will be issued by the Department or the Agency, after the travel commences, upon receipt of the report required in 3 FAM 2445 .  Travel will be chargeable to the current applicable appropriation.  Other fiscal data will be supplied by Washington, DC.  Movement of household effects and shipment of automobiles must not be authorized until receipt of instructions from the Department or Agency.

14 FAM 535.2  Travel under Authorized/Ordered Emergency Evacuation

14 FAM 535.2-1  General

a. When the Under Secretary for Management (M) makes a determination that an emergency exists at a post requiring the evacuation of official U.S. citizen employees, official travel and transportation may be authorized for the employees, their eligible family members, and effects from post of assignment to place designated in the travel orders, and thence to post.

b. When M makes a determination that an emergency exists at a post requiring the evacuation of Foreign Service national employees, official travel may be authorized for the Foreign Service national employees and their immediate families to the nearest practicable place for the duration of the emergency.

c.  The authorizing officer at post must issue individual or blanket travel authorizations (see 14 FAM 628 for shipment and storage of household effects (HHE)).

14 FAM 535.2-2  Travel Authorizations under Authorized/Ordered Emergency Evacuation

a. State only :  The authorizing officer at post must issue individual or blanket travel authorizations.  Each authorization must cite the names of the persons traveling.  In addition to the usual post distribution of copies, the authorizing officer must furnish information copies of all evacuation travel authorizations to the:

(1)  Bureau of Global Talent Management (GTM/CDA/AD);

(2)  Travel and Transportation Management Division (A/LM/OPS/TTM);

(3)  Appropriate regional bureau; and

(4)  Office of Accounting Operations (CGFS/F/AO).

b. Commerce only :  The authorizing officer must furnish evacuation travel authorization copies to the:

(1)  Office of Foreign Service Human Resources (USFCS/OFSHR);

(2)  State's Travel and Transportation Management Division (A/LM/OPS/TTM); and

(3)  Office of Planning and Management.

c.  USAGM only :  The authorizing officer must furnish evacuation travel authorization copies to the:

(1)  Office of Foreign Service Personnel (D/OHR);

(2)  Office of Administrative Operations Division (M/AO); and

(3)  Appropriate administrative office.

d. USDA/FAS only :  The authorizing officer must furnish evacuation travel authorization copies to the:

(1)  Foreign Agricultural Affairs/International Services Division (USDA/FAS/OFSO/ISD); and

(2)  State's Travel and Transportation Management Division (A/LM/OPS/TTM).

e. APHIS only :  The authorizing officer must furnish evacuation travel authorization copies to the International Services/Administrative Services/Travel Section.

f.  U.S. Despatch Agents :  The Department's or Agency's transportation office will ensure that the appropriate U.S. Despatch Agent receives a copy of the evacuation order or request and authorization for use in clearing the employee's shipment(s) through U.S. Customs.

14 FAM 535.2-3  Prohibitions Against Official and Personal Travel to Posts under Authorized/Ordered Emergency Evacuation

See 3 FAM 3770 regarding requirements and restrictions for official and personal travel to posts under authorized departure, ordered departure, suspended operations, contingency operations, and posts designated partially unaccompanied or unaccompanied.

14 FAM 535.3  Emergency Visitation Travel

The cost of emergency visitation travel in connection with the serious illness, injury, or death of an immediate family member is performed in accordance with the provisions of 3 FAM 3740 .

14 FAM 535.4  Visitation Travel

14 FAM 535.4-1  Authorization

Travel of an employee or eligible family member may be authorized and performed in accordance with regulations in 14 FAM 523.2-1 , subparagraph f(1)(h), and in 3 FAM 3730 .

14 FAM 535.4-2  Travel to Countries With Closed Posts Or No U.S. Diplomatic or Consular Relations

See 3 FAM 3780 regarding requirements for official and personal travel of employees to countries with which the United States has no diplomatic or consular relations or where all U.S. posts have been closed, and where travel may be prohibited or restricted.

14 FAM 536  SPECIAL TRAVEL

14 FAM 536.1  Voluntary Separate Maintenance Allowance (SMA) Travel

14 FAM 536.1-1  Authorization

a. Travel may be authorized for all eligible family members for whom SMA is granted under Section 260 of the Department of State Standardized Regulations (DSSR).

b. Per 3 FAM 3232.3-3 , only one change of status of SMA for each family member will be permitted for a single tour of duty.  See DSSR 264.2(b) regarding change in status in an evacuation.

14 FAM 536.1-2  Authorized SMA Location(s)

a. The following SMA travel at U.S. Government expense may be approved to authorized location(s):

(1)  When the employee's point of origin is in the United States, an employee's family members may remain at the employee's last official duty station in the United States, or travel to the home leave location designated on Form OF-126 or Washington, DC when the employee is transferred to a foreign post of assignment;

(2)  When an employee transfers from one foreign post of assignment to another, an employee's family member(s) may travel to the home leave location designated on Form OF-126, Foreign Service Residence and Dependency Report, or Washington, DC;

(3)  If an SMA is granted during an employee's tour of duty abroad, the employee's family members may be authorized travel to the home leave location designated on Form OF-126, or Washington, DC.

b. For shipment of household effects under SMA Grant, see 14 FAM 613.7 .

14 FAM 536.1-3  Alternate SMA Location

a. U.S. family members traveling to an alternate SMA location in the United States (see definition in 14 FAM 511.3 ) may do so on a cost-constructive basis.  The maximum amount of reimbursement is the cost required to move the family members from the authorized point of origin to the authorized SMA point.

b. Foreign location: An employee's family members traveling to a foreign SMA location may do so on a cost-constructive basis.  The maximum amount of reimbursement is the cost required to move the family members from the authorized point of origin to the authorized SMA point.

c.  Should an employee's SMA grant be terminated due to the employee's subsequent transfer to another post of assignment while the family members are at a foreign location, the employee will be responsible for the payment of excess travel costs involved in relocating the family members to the new post of assignment.  The excess travel costs, if any, must be determined through a constructive cost analysis that compares the travel cost of the employee's eligible family members that would have been authorized from an authorized SMA location to the next post of assignment compared to the amount that is actually incurred.  Any amount in excess of the amount allowable is payable by the employee.

d. Family members in a foreign alternate SMA location have no diplomatic status or privileges.

14 FAM 536.1-4  SMA Travel Financed by Employee

An employee who initially pays the costs of advance travel of family members may subsequently claim reimbursement of travel and transportation expenses if the agency later authorizes an SMA grant for the affected family members.  An employee may not recover a greater amount than would have been incurred had the U.S. Government procured the travel (see 14 FAM 544.2 , paragraph c).

14 FAM 536.2  Death of U.S. Citizen Employee

The following applies to an employee abroad, on domestic assignment, or on TDY.

14 FAM 536.2-1  Expenses in Connection with Remains

a. Following the death of a Foreign Service employee or EFM while in a foreign area, expenses may be authorized for the reasonable cost of preparing remains including the cost of embalming, clothing, cremating, casket, or container suitable for shipment to the place of interment; expenses incurred in complying with local and U.S. laws; and transportation of remains from place of death to the employee's authorized separation address. Transportation of remains to any other place in the United States or its territories as designated by the next-of-kin may be done on a cost-construct basis against the authorized separation address, by surface, or by air.  For shipment of remains to a foreign country, see 14 FAM 536.2-4 .

b. Following the death of a Foreign Service employee or EFM while on assignment in the United States or a non-foreign area, expenses may be authorized for transportation of the remains from place of death to the employee's authorized separation address. Transportation of remains to any other place in the United States or its territories as designated by the next-of-kin may be done on a cost-construct basis against the authorized separation address, by surface, or by air.

c.  For Civil Service employees, refer to FTR, chapter 303.

14 FAM 536.2-2  Family Travel Expenses

Expenses may be authorized for the travel of the family from the last place at which dependents resided and traveled at U.S. Government expense, to any place in the United States designated by the next-of-kin as separation residence or place of interment.  For travel to foreign countries, see 14 FAM 536.2-4 .

14 FAM 536.2-3  Transporting Effects

Expenses may be authorized for the transportation of effects from the last post of assignment, and safe haven if effects are located there, and from any place where effects are stored at U.S. Government expense, to separation residence designated by the next-of-kin.  For transportation to foreign countries, see 14 FAM 536.2-4 .

14 FAM 536.2-4  Foreign Destinations

Actual authorized expenses may be authorized for travel, transportation of effects, and/or shipment of remains to a foreign country and are allowed up to the constructive cost to place last designated by employee as separation residence.  Place of interment may differ from residence for travel and transportation of family.  When one location or the other is in a foreign country, this does not limit the next-of-kin's discretion in designating an authorized location in the United States for either interment or travel and transportation of family.  Authorized expenses may be incurred at any time within 12 months following the date of death, unless the time limitation is waived by the GTM/EX Director or USAID Executive Officer for USAID staff.

14 FAM 536.3  Family Member Death

a. This section applies when the employee is assigned abroad or is on domestic assignment.

b. Actual expenses may be authorized for round-trip travel of a family member and for transportation of remains to the separation address or on a cost-constructive basis to any other point in the U.S. or foreign country.

14 FAM 536.3-1  Expenses in Connection with Remains

See 14 FAM 536.2 .

14 FAM 536.3-2  Family Travel Expenses

Travel expenses are authorized for an employee or an eligible dependent to accompany the remains of a family member to the place of interment in the United States or abroad and return to the duty station (see 3 FAM 2550 ).

14 FAM 536.3-3  Transporting Effects

Transportation of effects is not authorized in connection with a family member death.

14 FAM 536.4  Travel and Transportation Expenses Authorized in Connection with Deaths of Locally Employed (LE) Staff when in Temporary Duty (TDY) Travel Status

Travel and transportation expenses are authorized when a LE Staff dies at a post abroad to which that LE Staff has traveled at U.S. Government expense.  Types of expenses authorized are detailed below.

14 FAM 536.4-1  Expenses in Connection with Remains

Expenses in connection with remains are authorized only as prescribed by 5 U.S.C. 5742, and within made available to the post.  The chief of mission must determine the payments to be made.

14 FAM 536.4-2  Transportation of Effects

Transportation of effects is authorized from the TDY post where death occurred to the LE Staff's post of employment.  Payments are to be made from allotments made available to the post.

14 FAM 537  through 539 unassigned

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Jarace Walker getting more chances for Indiana Pacers as feel for the game improves

Walker has been much better of late

• Author: Tony East

INDIANAPOLIS — After being out of the Indiana Pacers rotation for much of the season, rookie forward Jarace Walker has played in 12 of his team's past 17 games. And while at first he was needed due to injuries, Walker is now earning rotation minutes for the blue and gold.

The 20-year old was unproven early in the season. He would gamble often on defense, which left him out of position. Walker couldn't quite keep up with the speed of the game. His reads were too slow, so it was hard to involve him in actions on either end of the floor.

That is usually how things go for a first-year player in the NBA. Their first few appearances are full of ups and downs. Walker is growing past that. The eighth overall pick in the 2023 draft has been much more effective in his recent outings, and it is clear that he has made progress throughout the season.

"He gets better all the time," Pacers head coach Rick Carlisle said of Walker during his team's recent road trip. "More physical. Better understanding of leverage. More solid defensively. Learning what we need from him offensively. Just working at the adjustments."

Walker started to get more opportunities as injuries piled up. In late February, both Aaron Nesmith and Doug McDermott were sidelined for the blue and gold. Walker grabbed spot minutes during that stretch, including 26:41 of playing time in New Orleans on March 1.

Nesmith returned around that time, but then the Pacers lost reserve ball handler Bennedict Mathurin for the season. The team still needed Walker to play, and sometimes play often. He was going to be in the rotation a few times.

Some nights, it looked rocky. In Orlando earlier this month, for example, the Houston product played for just three minutes in a win. In other games, though, Walker added a ton of value. He defended DeMar DeRozan when Indiana hosted Chicago earlier this month, and he was solid when the Minnesota Timberwolves came to Indianapolis a few days prior.

Walker acknowledged after that outing against the Bulls that his confidence level has risen. Between playing more often and having more important assignments, it's clear that Indiana trusts him to contribute in ways that they didn't earlier in the season, and Walker is more self-assured with those roles.

"The confidence comes from the work you put in every single day," Walker said that night. He had 10 points and four rebounds, and the Pacers outscored the Bulls by 14 in his minutes. He frequently was given the assignment of containing DeRozan, something that wouldn't have been an option in the first few months of this campaign.

"If I was guarding DeMar early in the season, I probably would have fouled out," the rookie said after the game. He can feel his progress.

Walker played for almost 10 minutes in the Pacers next game when they hosted the Brooklyn Nets, and his opportunities continued as the blue and gold embarked on a road trip over the past week. The five-game, eight-day trek was going to be taxing. Reserves were going to play and be relied on during that stretch.

That became even more true on Monday when Nesmith was dealing with a knee injury and missed Indiana's tilt with the LA Clippers. It was the second night of a back-to-back for the Pacers. Walker was going to be needed on the wing, and often.

He was up for the task. The Baltimore native played for 29:23, a career high in minutes. He defended star players like Kawhi Leonard and Paul George without making too many mistakes. All of his shots went in — he finished with eight points on 3/3 shooting.

Walker also added four rebounds and a career-high seven assists. He was reading the game well, and the Pacers couldn't take him off the floor. He played the entire second quarter and started the second half after not opening the game for the team. Carlisle couldn't afford to get Walker off the floor and lose his effectiveness.

The 20-year old told AllPacers in Detroit that the game is finally slowing down for him. "For sure. I feel like early on, the game was a lot faster than I anticipated," He said. Now, with more minutes, he can feel what is going on more effectively.

Everything is easier when the game slows down, which Walker explained in more detail. "I think it's just like the literal speed. You can watch it, but I feel like until you're out there, the speed that players go at, the intensity that they go is a different level," he shared. He believes his offensive reads are better and his recognition of various patterns on the defensive end have improved. He doesn't have to think as much.

"I feel like the more time out there, I just kind of try to hoop, play my game," he said. The more the rookie plays, the more confident he feels, and Walker believes he has gained the trust of his teammates.

Since Mathurin's season-ending injury, Walker is averaging 3.5 points, 2.3 rebounds, and 1.3 assists per game. Those numbers aren't eye-popping, but they are improvements and are coming far more consistently. He's also been much better on the defensive end and is shooting 40% from deep in that stretch.

In a season full of ups and downs, Jarace Walker is finally turning a corner. During the Pacers last game — a road loss to the Chicago Bulls — Walker was in the playing rotation despite both McDermott and Nesmith being healthy. He had an off night, but that was the first time that substitution pattern happened all season.

"He's going to be a tremendous player for us," Carlisle said of Walker. The lottery pick is starting to show flashes of being that contributor.

• Tyrese Haliburton on his recent three-point shooting for Indiana Pacers: 'It's just a little slump right now'.  CLICK HERE .
• Myles Turner sets Indiana Pacers franchise record for total blocks: 'Hopefully it'll be there for a long time'.  CLICK HERE .
• Isaiah Jackson returns home and dominates to help Indiana Pacers beat Detroit Pistons.  CLICK HERE .
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Many travel nurses opt for temporary assignments because of the autonomy and opportunities − not just the big boost in pay

Assistant Professor of Communication Studies, University of Houston-Downtown

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Ivan Gan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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Travel nurses take short-term contracts that can require long commutes or temporarily living away from home. Time and again, they have to get used to new co-workers, new protocols and new workplaces.

So why would staff nurses quit their stable jobs to become travel nurses?

Well, for one, they get bigger paychecks . But U.S. nurses have other rationales besides making more money, according to a study I conducted .

To do this research, I interviewed 27 registered nurses based in different places.

Many of the people I interviewed disclosed that they left permanent positions to combat burnout. Although they welcomed the bump in pay, travel nursing also gave them the autonomy to decide when and where to work. That autonomy allowed them to pursue personal and professional interests that were meaningful to them, and it made some of the other hassles, such as long commutes, worth it.

On top of earning more money, travel nursing “gives you an opportunity to explore different areas,” said a nurse I’ll call Cynthia, because research rules require anonymity. “When you actually live there for three months, it gives you a chance to really immerse yourself in the area and really get to know not just the touristy stuff, but really hang out with the locals and really be exposed to that area.”

Other study participants said they enjoyed the novelty and educational opportunities.

“You don’t get bored or stuck in a routine,” Michelle said. “You’re always trying to learn new policies at the new hospital that you’re in, learning about the new doctors, nursing staff, new ways of doing things, where things are located. That helps keep me from feeling burned out so quickly.”

Said Patricia: “I want to see how other operating rooms across the country do things and how they do things differently. I do learn a lot of things going from place to place.”

Why it matters

A growing number of U.S. nurses were obtaining temporary assignments before the COVID-19 pandemic began.

But travel nursing became much more widespread in 2020, when hospitals were scrambling to keep their staffing levels high enough as millions of Americans were becoming infected with the coronavirus, straining capacity in many communities.

While compensation varies widely, the median pay of registered nurses in 2022 was US$81,220 , about 35% less than the $110,000 that registered nurses who traveled earned .

At the height of the COVID-19 pandemic, travel nurses could earn an even bigger premium . Many were paid twice as much as staff nurses.

Once the number of Americans with severe symptoms fell, that premium declined too . But there are still over 1.7 million travel nurses in the U.S. Hiring them is one of the main ways that hospitals cope with a long-term shortage of nurses .

But nurses with permanent jobs can get aggravated by this arrangement when they learn how much more travel nurses earn for doing the same work, as I found through another research project .

What other research is being done

Research supports a widely reported trend: More Americans have temporary jobs and freelance employment than in the past.

While travel nurses can help hospitals, nursing homes and doctors’ offices meet staffing needs, there are signs that patients don’t always fare as well with their care.

And a Canadian study found that when hospitals let staff nurses work part time and offer other alternative arrangements, their retention rates may rise .

The Research Brief is a short take about interesting academic work.

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Power ranking Sweet 16 teams in the men's 2024 NCAA Tournament based on March Madness odds

And then there were 16.

The first week of March Madness concluded on Sunday night with the final game in the round of 32 . Sixteen teams remain to compete in the regional semifinals – better known as the Sweet 16 – later this week.

Since original odds for the men's NCAA Division I tournament came out following Selection Sunday, not much has changed at the top. All four No. 1 seeds remain in the tournament as well as all four No. 2 seeds, and UConn still reigns supreme as the clear favorite to win the title.

Here are the latest power rankings for the 16 teams that remain in the tournament according to their current odds to win the national championship, per BetMGM .

March Madness takeaways: Upsets, Sweet 16 chalk and the ACC lead key points from men's NCAA Tournament

FOLLOW THE MADNESS: NCAA basketball bracket, scores, schedules, teams and more.

March Madness power rankings: Sweet 16

1. uconn (+200).

The Huskies entered the tournament as its No. 1 overall seed, and they've done nothing but back up that placement.

UConn dominated both of its March opponents in the first two rounds, defeating No. 16 Stetson 91-52 and No. 9 Northwestern 75-58. The last game the Huskies won by single digits was its Big East tournament semifinal victory over St. John's. They will play No. 5 San Diego State in the Sweet 16 on Thursday night.

2. Houston (+500)

Houston survived a close upset attempt from Texas A&M in the second round on Sunday night after the Aggies hit a buzzer beater at the end of regulation to force overtime.

The Cougars' dominance in their first season in the Big 12 and excellent defensive performances all season have them set up well for a deeper tournament run. They're in the Sweet 16 now and will play No. 4 Duke on Friday.

3. Purdue (+650)

This is not last year's Purdue team. The Boilermakers, who lost to No. 16 Fairleigh Dickinson in the first round of the 2023 NCAA Tournament, won each of their first- and second-round games by over 25 points.

Purdue took down No. 16 Grambling State in a 78-50 effort before drubbing No. 8 Utah State, 106-67, in the second round. The Boilermakers take on the No. 5 Gonzaga Bulldogs in the Sweet 16 on Friday.

4. Arizona (+800)

Not only does Arizona have the best odds of the four No. 2 seeds that remain in the tournament, the Wildcats currently hold better odds to win it all than the No. 1 seed in their region.

Arizona took care of business against its opponents in the first two rounds, defeating No. 15 Long Beach State 85-65 in the first round and No. 7 Dayton 78-68. The Wildcats will play No. 6 Clemson in the Sweet 16 on Thursday.

5. North Carolina (+1000)

How about the Research Triangle?! North Carolina, Duke and N.C. State have all made it to the Sweet 16 one year after none of them did. The No. 1 Tar Heels are among favorites to win it all after finishing as ACC tournament runners-up (to N.C. State) and two early victories in March Madness.

North Carolina took out No. 16 Wagner in a 90-62 win and defeated Tom Izzo's No. 9 Michigan State with an 85-69 victory. They play No. 4 Alabama in the Sweet 16 on Thursday.

Men’s March Madness Sunday recap: UConn, Duke, Houston, Purdue reach Sweet 16

6. Tennessee (+1200)

7. marquette (+1600), 8. iowa state (+1800), t-9. duke (+2500), t-9. gonzaga (+2500), t-9. creighton (+2500), 12. illinois (+2800), 13. alabama (+4000), 14. san diego state (+6600), 15. clemson (+8000), 16. n.c. state (+10000), how to watch ncaa men's basketball march madness 2024.

All games will be broadcast across CBS, TBS, TNT and TruTV. Here are additional streaming options to watch all the action on your devices.

• Stream through Paramount+
• Stream through HULU with Live TV
• NCAA March Madness Live app
• Stream through DirecTV Stream

How to watch March Madness: Watch all tournament games with a subscription to fuboTV

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Cold weather pay offered to incentivize assignments to North Dakota bases

WASHINGTON (KMOT) – Airmen from other parts of the country sometimes lament assignments in North Dakota due to the cold winters, but the Air Force is starting a new incentive program for servicemembers who have to “come North.”

The Air Force is rolling out a special cold weather duty pay for airmen and guardians assigned to bases where the temperature can drop below -20 degrees Fahrenheit.

This includes Minot Air Force Base, Grand Forks Air Force Base and Cavalier Space Station.

The idea is to help offset the costs of cold-weather items, such as gear, snow tires, engine block heaters and emergency kits for your car.

Pay will begin July 1, and the Air Force will announce specifics on pay amounts closer to the date.

Both North Dakota Senators John Hoeven and Kevin Cramer, along with Alaska Senators Lisa Murkowski and Dan Sullivan, recently sent a letter to the Secretary of the Air Force to implement the program.

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Details on April 8 partial solar eclipse in ND; what to expect in the path of totality in other parts of the country

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