Travel Behavior

# Introduction

Trip-Based Models, Activity-Based Models and Freight Models rely upon assumptions about human travel behaviors conducted by individuals, groups, firms, or households. A fundamental assumption in travel behavior is that travel is a derived demand resulting from the separation of desirable activity locations across space at their availability at specific times and is driven by the need for individuals to engage in activities at those locations to satisfy their own basic personal needs or desires. A common representation of these needs is given by Maslow[1] as the hierarchy of needs. These needs can generally be thought of as driving travel demand as individuals move through space and time engaging in activities like work (which satisfies the need for resources), socializing (belonging and esteem), recreation and leisure (self-actualization), etc. The process whereby individuals organize their day to satisfy these needs as best they can given space-time constraints, cognitive limitations, the needs of others, etc. can be thought of as Travel Behavior.

As can be seen, travel behavior is a broad topic that touches on almost every aspect of Travel Demand modeling and forecasting in some way. Kostas Goulias has stated that travel behavior modeling:

...refers primarily to the modeling and analysis of travel demand on the basis of theories and analytical methods from a variety of scientific fields. They include, but are not limited to, the use of time and its allocation to travel and activities, the use of time in a variety of time contexts and stages in the life of people, and the organization and use of space at any level of social organization, such as the individual, the household, the community, and other formal or informal groups.[2]

Some other basic assumptions about travel behaviors used in most models include:

  • People experience negative utility for additional time and money spent travelling. Humans have limited time in their days and trade-off travel for participating in other possible daily activities. Travelers will choose shorter time path, all else being equal. Similarly, travelers will chose lower cost ways of travel over higher cost ways.
  • Individuals are rational decision makers who seek to maximize their utility. Travel models tend not to model irrational choice making in practice, although satisficing models of behavior based on behavioral observations have been made.
  • An individual with a higher income will tend to be less sensitive to travel cost than a lower income individual.
  • Travelers are attracted to locations with a large amount of households and jobs and will tend to travel further distances to these locations than lower density areas.
  • Single occupancy vehicle travel is generally preferred over transit, even after accounting for time and cost of travel.

Many travel behaviors change over time and across cultures. For this reason, Travel Survey Data is collected on a periodic basis to understand the local and temporal context of travel behavior. Modelers must be careful not to imbed behavioral assumptions into models that may change over time when forecasting.

To the extent that is possible, travel behaviors should be treated often as sensitivities in the model so that a range of scenarios are predicted, realizing that certain behaviors are not precise mechanical operations, but malleable based on many possibly unknowable factors. One role of the modeler, then, is to identify how travel will be impacted if certain behavioral trends continue or cease.

Activity-Based Models depict the time tradeoffs among activities and travel in the day.

There are several recent papers and reports which present fairly comprehensive overviews of current trends in travel behavior research, including Emerging Issues in Travel Behavior Analysis by Pendyala and Bhat, and Travel Behaviour: A review of recent literature by Curtis and Perkins which are both available online. A more recent review by Buliung and Kanaroglou is also available but requires a subscription to access. These reviews taken together provide a solid foundation to understanding the current state of travel behavior research

# Topics in Travel Behavior

# Representations of Decision Making Behavior in Travel Modeling

Decision-making is a central element of traveler behavior modeling. Many of the behaviors represented in travel demand model are directly related to a decision making process - from choosing travel modes to selecting routes to reach a destination. The way in which these decisions are modeled, however, varies greatly for different decisions and in different model frameworks. The most common form that decision making behavior takes is that of the discrete choice model. However, many other decision making behaviors are utilized in travel models, including heuristic methods, processes derived from artificial intelligence such as the computational process model.

# Activity-Travel Planning and Decision Making Behaviors

Activity-travel planning behaviors generally refers to the behavioral processes by which individuals plan, schedule and implement their day-to-day activity and travel plans. Activity-travel planning is a broad topic which encompasses many different traveler behaviors, from the activity conception or generation process, to the decision-making processes by which the activity plan is carried out. These behaviors are represented in many different ways in various conceptional models of activity planning behavior, and are implemented in most activity-based models to some extent.

# Joint Travel Behavior

Joint Travel Behavior refers to how people choose to travel when considering the travel of other household members or persons in their social networks. Children under driving age need to be driven to activities by parents, which requires coordination of household schedules. Household members often need to decide how to share vehicles to conduct daily activities. Some activities are more likely to be conducted with other people, like eating a meal or socializing, whereas other activities are more likely to be conducted alone like commuting to work.

# Travel Behavior of Diverse Populations

# Using policy to affect travel behavior

# Long Distance Travel Behavior

# Historical and Political Context impacts on travel behavior

# Travel Behavior Definitions

Definitions for common terms observed in the travel behavior field.

# Travel Behavior Resources

A selection of papers, presentations and reports discussing the above topics

# Other Resources

TRB supports a committee on travel behavior and values. The committee is concerned with promoting research and disseminating research results on traveler values, attitudes, and behavior. Traveler values and attitudes refer to motivational, cognitive, situation and disposition factors determining human behavior. Traveler behavior refers primarily to the modeling and analysis of travel demand, based on theories from a variety of scientific fields. These include but are not limited to time use and activity-based approaches, longitudinal methods, and spatial behavior at any level of aggregation (e.g., individual, household, community, and so forth). The committee serves as a forum for the development, testing, and dissemination of new interdisciplinary methods of inquiry 1. If you are interested, please visit their TRB Traveler Behavior and Values committee website

Another significant resource in the field is the International Association of Travel Behavior Research. This group consists of the leading researchers in the field of traveler behavior. It hosts triennial conferences where the latest research in field is presented and publishes selected works from each conference in a conference book. More information on IATBR can be found at

# References

  1. Maslow, A (1954). Motivation and personality. New York, NY: Harper. p. 236. ISBN 0-06-041987-3. ↩︎

  2. Goulias, Kostas ↩︎