COMPARISON OF THE USE OF COBA, CONTRAM AND TRAFFICQ FOR THE ECONOMIC APPRAISAL OF ROAD IMPROVEMENT SCHEMES IN URBAN AREAS

COBA, CONTRAM and TRAFFICQ are three programs used to estimate future traffic conditions consequent upon changes to a road network. The study reported here is an initial examination of their applicability to the economic appraisal of road improvement schemes in urban areas. Only COBA performs an economic evaluation, and so the essential question examined here is whether the traffic evaluations are equivalent, since economic evaluation is subsequent to this issue. An examination of the theoretical bases of each model thus precedes a series of tests designed to bring out clearly some of the differences between the models. Since each model was designed for a different purpose and within a different context, and has its own theoretical basis, it is not surprising that significant differences in responses to changes are found, even to the extent of differences in direction of response. More work therefore needs to be done to produce a model suitable for prediction of traffic conditions in urban areas for purposes of economic appraisal. Such work should if possible include comparison between model estimates and real data. (TRRL)