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How Can A Scheme Be Designed?
As explained in the previous chapter, it is common to consider URUC as part of a package of complementary transport measures aimed at improving the overall provision of transport in a city. The charging will generate the revenue necessary to fulfil the ambitions of the overall urban strategy. Judgmental approaches to cordon design
The performance of any road pricing cordon or boundary will be affected by the combined effects of a reduction in traffic entering the area and an increase in traffic bypassing it. While congestion will be reduced within the area, it might well be aggravated outside it. Since these conflicting impacts will depend on both the topology of the road network and the pattern of demand for its use, it is difficult to offer general advice on cordon location. All that is known is that the benefits of road pricing, usually measured in terms of welfare economic impacts, are critically dependent on the choice of cordon (May et al, 2002).
Yet it has been observed that there has actually been very little technical advice on the best location for such boundaries. Most designs are based on a mix of professional and political judgment, with little or no assessment of whether alternative locations would be more effective.
A study on judgmental approaches to cordon design among six UK local authorities at different stages in the development of road pricing proposals is reported in May et al (2002). It involved an initial questionnaire and a subsequent in-depth interview with a responsible transport planner. The study covered the context of the proposal, the objectives of the scheme and the detailed design process. A general finding was that the context and objectives had little impact on detailed design. The key elements in the design process were to avoid adverse impacts and to gain public acceptance. The practical aspects were generally less important. The criteria which emerged from the survey are listed below, under the same three headings.
- Avoid adverse impacts
- Gain public acceptance
The avoidance of visual intrusion, resulting from the technology to be used and signs and markings, is a concern especially in the historic areas of city centres. This was an issue in the proposed Edinburgh scheme, as well as for the schemes implemented in Rome and London.
Theoretical approaches to cordon design
Recent research on Cordon Design has involved two separate methods. The first of these uses an application of genetic algorithms to represent design options and to highlight those which are most effective. The second provides a short cut method which is analytically less complex and involves the planner directly in the design process. Both have been shown to provide two- to three-fold improvements in performance over judgmental designs. They are not, however, intended to supplant the need for professional and political judgment; rather they are offered as design tools which will help to focus such judgment on those designs which are likely to be technically the most effective.
Further details on current research on optimal designs by a genetic algorithm based approach and a “short cut” approach are given in Appendix A in this report.
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