A Modelling Approach
Edited by Bruno De Borger and Stef Proost
Chapter 10: Speed-flow relationship and feasability of road-pricing technology
10. Speed–ﬂow relationship and feasibility of road-pricing technology Margaret O’Mahony and K.J. Kirwan 10.1 INTRODUCTION This chapter is divided into two parts. In the ﬁrst, the research into selecting the most appropriate speed–ﬂow relationship for use in the development of the TRENEN models is described. The selected function type was used in all of the applications. In the second part of the chapter the current state-of-the-art in road-use pricing is summarised including indications of likely future developments and uses of technology. The ﬁnal part of the chapter describes a road-use pricing trial underway in Dublin which is using the TRENEN evaluations of external costs as the road-use charging levels. 10.2 SPEED–FLOW RELATIONSHIP RESEARCH OBJECTIVES The ﬁrst objective was to quantify the external costs of congestion for which it was necessary to obtain a function describing the relationship between average speed on an urban network and the overall level of demand for car travel. The second objective was to examine the possibility of estimating the function from network parameters, such as, for example, junction capacities and number of junctions per unit length of network. 10.2.1 Link-based Speed–ﬂow Relationships Link-based speed–ﬂow relationships have been used mainly in engineering studies and for economic cost–beneﬁt analysis. The relationships describe speeds and associated time costs at each level of traﬃc ﬂow and are usually deﬁned for road sections of homogeneous properties with few junctions. The Highway Capacity Manual (TRB, 1992) outlines the standard approach for deriving...
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