Dynamic Traffic Assignment: Assessing Its Value as a Planning Support Tool in Arizona

Traffic modeling creates a mathematical model of a real-world transportation system, such as a highway network. Modeling is used to test the effects of network or traffic changes on travel time, delay, and related variables. The Arizona Statewide Travel Demand Model (AZTDM) simulates the interaction between people and the roadway system. It models travel behavior to prepare the forecasts used for highway design and transportation planning. Traffic assignment is the phase of modeling that assigns passenger and freight vehicles to a route between origin and destination. The AZTDM currently has a static assignment process, which represents average conditions over a long period, in contrast to the rapidity with which traffic levels can change in the real world. A recently developed technology, called dynamic traffic assignment (DTA), is designed to represent fluctuating traffic volumes and long trips on complex networks. The word “dynamic” refers to continuous change, reflecting the variation of traffic volumes both randomly and through a daily cycle. DTA may take a step beyond static methods (which focus on highway capacity) by helping ADOT evaluate and compare proposed modernization projects, which typically involve cost-effective improvements without major expansion of capacity. ADOT’s Long-Range Transportation Plan (LRTP) calls for this type of project to receive a growing share of state highway funds. If incorporated into the AZTDM, DTA may enhance ADOT’s understanding of existing and future travel behavior, enabling a more accurate modeling of traffic congestion and freight movement, as well as the testing of alternative solutions. However, ADOT does not know the extent to which DTA might improve the forecasting capabilities of the AZTDM. No research on DTA has been performed on the Arizona state highway system. Research Objectives: The objective of the research is to evaluate the feasibility — in terms of cost, accuracy, and integration with the existing static model — of creating a DTA tool to work with the AZTDM. The research will determine whether DTA can generate more useful data, thus improving ADOT’s ability to plan for modernization of state highways. The research will: • Identify the state of the practice in DTA. • Identify available open-source DTA software, develop and apply evaluation criteria, and recommend the product most effective for ADOT’s use. • Using the recommended software, determine whether implementing DTA is feasible at the state level in Arizona. o Test the performance of DTA and compare it with that of the existing AZTDM. o Show how, when, and where DTA may best be applied in Arizona. • If DTA is deemed feasible, provide an implementation plan that would use the specified open source software. • Identify major costs and benefits, particularly those involving personnel, training, and hardware/software.