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A C O M PA R I S O N O F S TAT I C A N D D Y N A M I C T R A F F I C A S S I G N M E N T U N D E R T O L L S 117 not be neglected. While the more realistic modeling may ers' ability to predict policies' impacts at a more disag- balance this additional time for long-term planning gregate level. Moreover, the use of link performance applications, the time needed to run a large number of functions limits its ability to model queues or spillover models may be prohibitive. Nevertheless, to reduce the effects between links due to congestion, which can be running time needed for DTA, the demand profiling captured using other formulations, such as the CTM. algorithm described above can be used to generate the With such improvements, investigations like this one data more quickly. could be extended to account for traffic dynamics under When static and dynamic assignment models were congestion management policies in greater depth. applied to the DFW network, TSTT was significantly higher when predicted by DTA, which indicates that stat- ic assignment models can significantly underpredict con- REFERENCES gestion levels due to changes in demand over the peak period. Additionally, the distribution of trips among dif- Daganzo, C. 1994. The Cell Transmission Model: A Dynamic ferent classes of roadways is significantly different Representation of Highway Traffic Consistent with the between the cell transmission model (used by VISTA) Hydrodynamic Theory. Transportation Research, Vol. 28, and the link performance function-based models (static No. 4, pp. 269287. assignment and the DTA approximator) because CTM Janson, B. N., and J. Robles. 1995. Quasi-Continuous Dynamic prohibits flows from exceeding capacities. VISTA pre- Traffic Assignment Model. In Transportation Research dicts significantly fewer freeway trips than static assign- Record 1493, TRB, National Research Council, Washington, ment or the approximator. D.C., pp. 199206. Further insights could be gained if the DTA approxi- Peeta, S., and A. K. Ziliaskopoulos. 2001. Dynamic Traffic mator in TransCAD provided additional capabilities. In Assignment: The Past, the Present, and the Future. Networks particular, the ability to extract path flows for each O-D and Spatial Economics, Vol. 1, No. 3, pp. 233265. pair and departure time would greatly enhance model-