The Department for Transport has published a research report on the effects of Smarter Choice programmes on the Sustainable Travel Towns (Darlington, Worcester and Peterborough). Measures implemented in the programme included personal travel planning, travel awareness campaigns, and promotion of walking, cycling and public transport. The programme was implemented over the period 2004-08 and comparisons made with data for comparable towns elsewhere.

The key finding is that, in the three towns, car driver trips by residents fell by 9% over the period (compared with 1% elsewhere) whereas the volume of traffic decreased by about 2%.  The disparity is attributed to population and employment growth, journeys by non-residents, and possibly induced traffic. Trips by bus, walking and cycling all increased markedly. The authors of the report infer that the observed travel behaviour change involves a combination of mode shift with unchanged destination, switch of destination and mode, and trip evaporation (not making the trip at all).

The report discusses the potential for measures to reduce car use to lead to induced traffic. The conclusion drawn is that induced traffic in the three towns would be expected to be very small, but this is based on the behaviour of the DfT’s National Transport Model (which in my view is not to be relied upon).  I would expect that if some virtuous people make less use of their cars, the reduced congestion would encourage other (less virtuous) people to take advantage of the increased traffic speed to make longer trips.  But whatever the position may be, the observed overall impact of the Smarter Choices programme on the volume of traffic seems substantially less than the impact on car trips made.  So the consequences for congestion and carbon emissions appear quite modest.