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Area Speed Flow Relationships:The Effect of Varying\ud Signal Capacity

By S. Shepherd


This paper is one of a series of ITS working papers and technical notes describing the\ud methodology and results of the EPSRC funded project "The definition of capacity in urban,\ud road networks : The role of area speed flow relationships". The objectioes of the project\ud were to investigate the interaction between vehicle-hours and vehicle-km within a network\ud as the demand for travel increases; to develop improved area speed flow relationships; to\ud use the relationships to explain the process by which networks reach capacity; and to assess\ud the significance for the evaluation of road pricing policies.\ud \ud The approach used was to collect the vehicle-hours and the vehicle-km directly from a\ud simulation model and thus create relationships between supply and demand in terms of\ud veh-hours/hr and veh-km/hr demanded and also between times per trip and trips\ud demanded.\ud \ud During the project two models were used. The first was a micro-simulation model called\ud NEMIS. This model was used on hypothetical networks ranging from single link to a six\ud by six grid and finally a ring-radial network. The networks were used to study the effects\ud of changes in OD pattern and the effects of varying capacity on the resulting speed flow\ud measures.\ud \ud The second model used was SATURN. This model was used to study the same ring-radial\ud as before and a full SATURN model of Cambridge. The SATURN results were then taken\ud one step further in that they were used to create an aggregate model of each network using\ud SATURN in buffer only mode. The related papers discuss issues such as network\ud aggregation. Note that the methodology and terminology was developed as the study\ud progressed and that in particular the method varies between application of the two distinct\ud models.\ud \ud The reader is directed to the attached appendix A for a full list of publications arising from\ud this project

Publisher: Institute of Transport Studies, University of Leeds
Year: 1995
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