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In recent years, there has been growing interest in a range of transport policy initiatives which are designed to influence people's travel behaviour away from single-occupancy car use and towards more benign and efficient options, through a combination of marketing, information, incentives and tailored new services. In transport policy discussions, these are now widely described as 'soft' factor interventions or 'smarter choice' measures or 'mobility management' tools. In 2004, the UK Department for Transport commissioned a major study to examine whether large scale programmes of these measures could potentially deliver substantial cuts in car use. The purpose of this paper is to clarify the approach taken in the study, the types of evidence reviewed and the overall conclusions reached. In summary, the results suggested that, within approximately 10 years, smarter choice measures have the potential to reduce national traffic levels by about 11%, with reductions of up to 21% in peak period urban traffic. Moreover, they represent relatively good value for money, with schemes potentially generating benefit: cost ratios which are in excess of 10:1. The central conclusion of the study was that such measures could play a very significant role in addressing traffic, given the right support and policy context. Acknowledgements: The support of the Rees Jeffreys Road Fund, which has enabled the preparation of this paper, is very gratefully acknowledged. In addition, the authors wish to gratefully thank the client team at the Department for Transport, all the different experts and practitioners working in this area who contributed to the study and the reviewers of this paper for their helpful comments.

Disparate evidence indicates that the provision of extra road capacity results in a greater volume of traffic. The amount of extra traffic must be heavily dependent on the context, size and location of road schemes, but an appropriate average value is given by an elasticity of traffic volume with respect to travel time of about -0.5 in the short term, and up to -l.0 in the long term. As a result, an average road improvement has induced an additional 10% of base traffic in the short term and 20% in the long term: individual schemes with induced traffic at double this level may not be very unusual, especially for peak periods. Induced traffic is particularly seen on the alternative routes that road improvements are intended to relieve.

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