REVIEW OF TRIP GENERATION STUDIES

This review is aimed at identifying whether trip generation studies can inform the wider planning debate and be of use in the achievement of PPG 13 objectives. It collates the state of knowledge on the factors determining trip attraction rates, modal split, travel times and trip lengths to specific types of land use. Current methodological practices are also reviewed. Trip generation studies show that the choice of mode is related to the locational attributes of the destination with city centre sites more frequently accessed by public transport than outer area destinations. Increasing decentralisation of both population and employment have exacerbated the swing towards car travel. For many land uses, the existing data on modal split is minimal or out of date and a significant number of studies have concentrated only on vehicular trips. Trip rates to office and retail sites are often estimated using inappropriate parameters. New data collection is required in order to derive robust estimates of newly generated, redistributed, pass-by, and linked trips. These would help towards the standardisation of traffic impact assessment. Data on travel distances and catchment areas should be obtained, since it is generator (rather than attractor) characteristics which are the major determinant of modal split. (A)