With assistance from a team of outside consultants, the PSRC is developing a next-generation activity-based travel demand model that will replace its current trip-based model prior to the next update of the regional transportation plan. The initial phase of the project, which included the development of a model system design plan and implementation of an activity generator, was completed in early 2009. The final phase of the project, which includes the development and implementation of remaining model system, was initiated in May 2009 and will conclude in 2012.

Key Design Features of the Activity-Based Travel Model

The basic organizing principle is an individual’s daily activity pattern, including such activities as going to work or school. Relationships are established between the state of the transportation system (i.e., level of congestion and/or accessibility) and the extent to which it influences substitution of activities outside the home with those inside the home. In other words, a highly congested transportation system will generate less demand for travel than a system with relatively little congestion, all else being equal.

The activity pattern-tour-trip segment relationship provides an individual’s overall travel behavior linked together by mode, destination, time-of-day, and other activities in the daily pattern. This approach differs from traditional trip-based modeling where trip segments are largely treated as unrelated events.

An activity-based model system is a highly disaggregate environment, representing the travel behavior of each individual and household separately. Disaggregation avoids the errors and biases associated with generalization and averaging that plague trip-based modeling and lends itself to a more realistic and accurate portrayal of travel behavior and demand.