This paper presents two different approaches to applying dynamic traffic assignment (DTA) method on statewide transportation planning and operations using the Maryland Statewide Transportation Model (MSTM). The MSTM was developed to analyze traffic issues throughout the state including traffic in rural areas, freight movements, long distance passenger travel and travel between the Baltimore and Washington Metropolitan areas. Our aim is to address challenges introduced by the regional/statewide models such as the need to accommodate long distance trips that typically traverse multiple geographies and multiple time periods, use of less detailed demand and supply representation due to almost prohibitively large network size, and model calibration and validation for real applications.
The first application is an analytical approach, developed as a proof of concept dynamic network model of MSTM using TRANSIMS Version 6 Router application. The model is able to track individual vehicles but does not simulate vehicle movements. Instead, volume-delay functions are used to update link delays. The model is validated against traffic counts and static assignment results. The results show that the analytical method used provides better estimates of dynamic traffic conditions, enables tracking the location of individual vehicles, and allows for the rerouting of vehicles in anticipation of congested conditions, while avoiding the need for detailed intersection information. The method also allows for computation within a reasonable amount of time. The validation results, despite the proof-of-concept nature, are comparable with the static assignment results and consistent with observed data.
The second approach is application of a queue-based, capacity-constrained DTA methodology to MSTM using DTALite. We propose a simplified simulation-based DTA method that can represent congestion dynamics i.e. queue buildup and bottleneck formation without the need for detailed network coding and signal timing input through use of macroscopic traffic flow models. The model’s capability of running large scale transportation models with 24 hour planning horizon is demonstrated on the MSTM, the first application of a simulation-based DTA to a statewide network of its size. The preliminary results suggest that the simplified DTA model provides fine-resolution spatio-temporal traffic performance measures compared to static models thus have the potential to provide more realistic decision and policy aid.
Keywords: Dynamic statewide models, analytical DTA, router-based assignment, TRANSIMS, statewide planning, dynamic traffic assignment, DTALite, queue-based assignment, capacity-constrained