Methods of evaluation of traffic restraint techniques

The common objective of traffic restraint policies is to make the best use of available resources, and the work 'restraint' enters as a result of current situations wherein traffic takes up too many of the constrained resources of environment and space. Restraint policies work by changing the observed behaviour of travellers in making modal choice, routing, and other travel decisions, including the decision to make the trip at all. Physical restraint schemes operate by prohibition or restriction of some or all classes of traffic in a given area whereas fiscal schemes operate by imposing extra monetary payments on traffic using road or parking space in a given area. Either type of policy will alter the balance between modes of travel, and may also affect the numbers of trips made. In order to determine the 'best' level of restraint to achieve optimal use of a given resource, it is necessary to decide on the objective function to be maximised (or minimised). As restraint operates by affecting behaviour, such a function must include valuations of the changes in behaviour observed. A measure of consumers' surplus must therefore be included and valuations obtained for comfort, convenience, and similar variables affecting behaviour. We can illustrate this approach to such an evaluation of restraint systems by two pieces of work carried out by the TRRL.