Virginia Transportation Modeling and Accessibility Program


What is Travel Demand Modeling?

A travel demand model is an analytical tool used to support the transportation planning process. It can be used to develop traffic forecasts, test alternative transportation scenarios, and evaluate transportation systems or policies. Models are developed and applied using demographic, survey, and transportation system data, which are used to build mathematical relationships and develop transportation networks that help answer questions such as:

  • When will a trip be made?
  • Where are people and goods traveling?
  • How are people and goods traveling?
  • Which route will they take to complete the trip?

Why is Travel Demand Modeling Important?

Travel demand models are fundamental to transportation planning and used to meet federal requirements in a number of areas. The travel demand forecasting process allows planners, engineers and other transportation professionals to estimate the amount of traffic that will exist on the transportation system in the future.  It further allows for the detailed assessment of specific project plans and designs, and their possible near-term and long-term impacts.  For larger transportation projects multiple alternatives are developed and compared in studies, and travel demand forecasting is a primary component of the alternatives’ development and comparison. 

Planners and engineers apply forecasting techniques to projects of all sizes, ranging from spot-improvements to the corridor level to regional and statewide transportation projects.  Travel demand models allow for regional (macroscopic) analysis of transportation networks. Regional differences also play a key role in the forecasting process.  Traffic patterns differ from dense urban centers to sparsely populated rural areas.  VDOT works closely with local and regional partners (such as metropolitan planning organizations and planning district commissions) to identify the population, employment, land use(s), development patterns and other factors that impact traffic distribution and growth during the development of travel demand models.

Applications of Travel Demand Models

Travel demand models are typically used to evaluate the impact of regionally significant projects- major widening, new locations or new intersections. Models are able to provide insights on how travel patterns could potentially change within a region with the implementation of proposed projects. Travel demand models are typically not used for detailed operational analysis- other models such as Highway Capacity Software, Synchro, CORSIM and VISSIM (microscopic models) are used to analyze projects such as turn lanes and traffic signals.

Modeling Development Responsibilities



What is Accessibility?

Accessibility analyzes how easy it is for a person or goods to access jobs, services, and facilities, and what it takes to travel to particular places. Accessibility is affected by travel time, travel cost, and the locations and service hours of desired destinations, as well as the person’s knowledge of and comfort with the choices of travel modes and service providers. , Accessibility metrics directly reflect this potential by combining network travel times with the locations and value of the many origins and destinations served by a multimodal transportation system. Planning for accessibility is important for making sure that there is good access to jobs and services such as shopping and health care.

Currently, VDOT had been applying the Accessibility analyzes as one components in the Smart Scale process to help the prioritization of transportation projects for funding. The Accessibility tool developed by Caliper had been used to generate accessibility scores based on Here network real traffic information.

Page last modified: March 25, 2023