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factor of the segment length, as is done in the BPR and exponential equations. In evaluating the speedâflow equations against theo- retical delays for hourly demands that exceed hourly capacities, only the Akcelik equation produced the expected delays due to oversaturated conditions at the downstream signal on a street segment. The other equa- tions significantly underestimated delay within the 1.00 to 2.00 v/c range, the BPR curve eventually surpasses the delay estimates produced by queuing theory and the Akcelik equation. ACKNOWLEDGMENTS The authors thank Deng-Bang Lee, Mike Ainsworth, Hong Kim, Gouxiong Huang, Huasha Liu, Teresa Wang, Dale Iwai, and many others at SCAG for their technical assistance, advice, and review throughout this project. Gouxiong Huang, in particular, advised the authors on how the link capacities for the model had been deter- mined. The authors also thank Verej Janoyan, Ray Andrade, and the other staff at the City of Los Angeles Department of Transportation for their assistance in pro- viding real-time traffic and speed data for city streets. Robert Dulla and Thomas Carlson of Sierra Research prepared the sampling plan for the study and the recom- mended sampling plan for monitoring of regional travel speeds on an ongoing basis in the future. Moses Wilson of Wiltech led the floating-car and traffic count data col- lection in the field. Chris Ferrell and David Reinke of Dowling Associates led the data analysis effort. REFERENCES Akcelik, R. 1991. Travel Time Functions for Transport Plan- ning. Australian Road Research, Vol. 21, No. 3, pp. 49â59. Highway Capacity Manual. 2000. TRB, National Research Council, Washington, D.C. Special Report 87: Highway Capacity Manual, 2nd ed. 1965. Highway Research Board, Washington, D.C. Traffic Assignment Manual. 1964. U.S. Bureau of Public Roads. Washington, D.C. 113URBAN ARTERIAL SPEEDâFLOW EQUATIONS FOR TRAVEL DEMAND MODELS Tr av e l T im e (h) SCAG Arterial Speed Study 0.6 0.5 0.4 0.3 0.2 0.1 0 Field Data Points Standard BPR Fitted BPR Classical Queue Theory Fitted Akcelik One-Hour Volume/Capacity Ratio 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 FIGURE 3 Speedâflow equations versus queuing theory.