As part of DVRPC's long range planning efforts, it is vital to have a firm understanding of current travel patterns and to produce forecasts of future highway and transit travel.
DVRPC forecasts future travel using a well-tested travel modeling process. The heart of this process is our transportation model, a package of computer programs that simulate regional travel behavior. With the model, our engineers and planners use a mathematical representation of the transportation system, along with data on population and economic activity and the principles of supply and demand, to estimate the travel behavior of people in the region. These models are often called simulation or travel demand models because they can be used to simulate the effect on traffic patterns (travel demand) of changes in the road or transit network (travel supply). Common travel patterns include a trip from home to work in the morning and a return trip home in the evening or a mid-day shopping trip.
A traditional four-step travel demand model is implemented at DVRPC.
In general, the four-step travel demand model proceeds in this way:
- The first of the four steps, trip generation, estimates the number of trips produced within specific areas - called traffic analysis zones (TAZs) - based on the population and employment characteristics of that area. Trips are generated for a number of different trip purposes.
- Trip distribution, which occurs next, determines where the trips produced in the first step will travel to by looking at the ease of getting to every possible location and draw of that area for that trip purpose. This establishes an origin and destination for each trip.
- The next step, mode choice, determines how a particular trip will be made, such as by driving a car, carpooling, riding transit or walking.
- Finally, the model determines which paths along the road or transit network each trip will take to reach its final destination. This step is called trip assignment. Paths are calculated to find those that minimize travel time and cost.
Forecasts that result from the travel demand model are used for many purposes, such as to determine the usage of a proposed transportation improvement (new road or transit line), the impact on area facilities of a change in roadway operational features or transit service features, or to evaluate the effects of the transportation system on regional air quality.
A travel demand model requires various data to produce forecasts. The systems planning unit collects and analyzes data on population and employment characteristics from the US Census Bureau and other sources. Traffic counts and transit ridership statistics are also important data for checking the accuracy of the travel demand model and for analyzing current and future travel trends within the DVRPC region.
Household Travel Surveys
Household travel surveys are used to obtain information about work and non-work trip generation, trip distribution, modal split, and average vehicle occupancy. Updated household travel information can be used for modeling purposes as well as transportation planning projects such as high occupancy vehicle lanes, bicycle, and pedestrian studies, welfare-to-work programs, and traffic control studies. The most recent household travel survey was conducted from March through December 2000 under the auspices of DVRPC and the South Jersey Transportation Planning Organization (SJTPO). SJTPO represents Salem, Cumberland, Atlantic, and Cape May Counties. Detailed information on the survey can be found in the report Transportation for the 21st Century Household Survey Travel Survey Results for the DVRPC Region.
Data from the survey can be found here. [2.63 MB .zip]
This data has been cleaned to remove personal information in order to protect survey participants.