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Extra traffic induced by road construction: empirical evidence, economic effects and policy implications

Goodwin, PB; (1998) Extra traffic induced by road construction: empirical evidence, economic effects and policy implications. In: ECMT,, (ed.) Infrastructure-Induced Mobility. European Conference of Ministers of Transport: Paris.

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Abstract

The balance of theoretical and empirical evidence indicates that additional traffic is induced by the provision of extra road capacity, due to a range of different behavioural responses. The amount of extra traffic will vary according to the specific circumstance, size of scheme, existing traffic congestion, geographical and economic conditions and availability of alternatives. In UK conditions, an average result for an average scheme may be of the order of 10 per cent extra traffic in the short run and 20 per cent in the longer run, with a range of 0-20 per cent in the short run and 0-40 per cent in the longer run. The extra traffic enjoys some benefits itself (hence increasing the calculated benefit/cost ratio of the road) but also erodes the benefit to other road users by shortening the period of relief from congestion (hence reducing the benefit/cost ratio). The net effect depends substantially on the level of congestion. Because of the non-linear nature of the relationship between traffic volume and speed, induced traffic reduces the overall value for money of a road scheme when conditions are more congested. Induced traffic also increases environmental damage. Therefore omission of induced traffic will always result in an overestimate of the environmental benefits of new capacity and usually result in an overestimate of the congestion benefits. These effects take place over several years. Research to monitor the effects of new road capacity cannot come to meaningful conclusions by observing only first-year effects. Evaluation procedures need to use dynamic concepts allowing for the speed of adjustment, not only a description of a final equilibrium. The policy consequences which follow depend on wider strategic issues, especially the pace of traffic growth due to factors other than new capacity. Currently, transport policy gives importance to environmental impacts, the need to ensure value for money from public funds and the need to protect economic benefits from erosion by congestion: in these circumstances, induced traffic reduces the effectiveness of a road-construction based transport strategy and gives additional emphasis to the importance of applying efficient methods of managing and reducing the growth in traffic

Type:Book chapter
Title:Extra traffic induced by road construction: empirical evidence, economic effects and policy implications
ISBN:92-821-1232-2
Keywords:balance, congestion, CONSTRUCTION, DAMAGE, Dynamic, dynamics, effectiveness, environmental impact, Equilibrium, evaluation, extra, Factors, generated traffic, growth, IMPACT, INCREASE, induced traffic, Money, nonlinear, Research, response, road, SACTRA, speed, STRATEGIES, Strategy, traffic, transport, transport policy, UK
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Civil, Environmental and Geomatic Engineering

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