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BREAKOUT SESSION Assignment Advances James Hicks, PB Consult, Inc. Richard Dowling, Dowling Associates Alexander Skabardonis, University of California, Berkeley Stephen Boyles, University of Texas at Austin Satish Ukkusuri, Rensselaer Polytechnic Institute S. Travis Waller, University of Texas at Austin Kara Kockelman, University of Texas at Austin A DYNAMIC TRAFFIC ASSIGNMENT matrices convert to discrete vehicle trips and assign MODEL BREAKDOWN departure times for trips. The traffic control input includes phasing and timing plans. DTA specifications James Hicks include the demand period, the simulation period, and the assignment interval. The link-time aggregation inter- James Hicks described the use of a dynamic traffic val, the results interval, the warm-up interval, and the assignment (DTA) model in Atlanta. He discussed the cool-down interval are other specifications. application of the VISTA DTA software package, the The input data for VISTA DTA includes the data requirements and specifications, and the analysis Atlanta regional highway network described as a link process and preliminary results. Volume 2 contains a table and a node table. Input tables also define the loca- paper on the topic.1 The following points were covered tion and operational characteristics of signalized inter- in his presentation. sections in the network, as well as an input table for the demand to be simulated for the network. The Georgia Department of Transportation is con- The vehicle simulation is based on the propagation ducting operational planning studies of different freeway of vehicles according to the cell transmission model net- sections in the Atlanta area. Microsimulation models of work links, which are divided into cells. Vehicles are freeway sections are being used to evaluate operational moved from cell to cell along links and between links. alternatives. A DTA model provides a method to calcu- The propagation of vehicles depends on the posted speed late realistic time-dependent flows through the areas. for the links, saturation flow rates, and jam sensitivities The DTA model uses input data from the regional travel for the links. demand modeling process and produces data required A 1-hour warm-up period was used in this analy- by the microscopic simulation method. sis. Three 1-hour analysis periods were used. These DTA model inputs include the regional highway analysis periods were 6:00 a.m. to 7:00 a.m., 7:00 a.m. network, regional trip matrices, and traffic control infor- to 8:00 a.m., and 8:00 a.m. to 9:00 a.m. Flows were tab- mation. The regional highway network includes posted ulated for these time periods and compared with speed and capacities by facility type. The regional trip observed 1-hour counts. A cool-down period sufficient to allow all vehicles to be simulated entirely from their 1 origins to their destinations was also used. See Hicks, J. E. A Dynamic Traffic Assignment Model Breakdown. In Conference Proceedings 42: Innovations in Travel Demand DTA models typically determine the equilibrium Modeling, Volume 2: Papers, Transportation Research Board of the solution by first identifying a feasible or reasonable path National Academies, Washington, D.C., 2008, pp. 101108. set and allocating flow between those paths in a manner 38