Evaluating Voluntary Travel Behaviour Interventions

Considerable interest in the policy of voluntary travel behaviour change interventions, known as by the generic name of TravelSmart®, has emerged. Measuring its effectiveness and determining its cost-benefit ratios is a major issue. Several difficulties arise in this process. First, it requires both a before and an after survey, sufficiently far apart to detect stable change in household travel behaviour. Second, it requires estimates of numbers of trips and activities, distance travelled by mode, time spent travelling by mode, and the modes of travel used. These are poorly reported in household travel surveys, introducing serious potentials for error in evaluation. Third, are issues relating to sample sizes to detect changes of the order of 5 to 10 percent in various travel behaviours, with acceptable accuracy. After discussing these issues in some detail, we describe a potential survey process, using GPS devices, that can overcome a number of the problems. We describe the information that can be obtained through the GPS and its associated prompted recall survey, demonstrating some of the benefits associated with this procedure. We conclude that evaluation is a significant issue that requires substantial funding to be done effectively, but that the GPS survey offers a high level of reliability in the information obtaine