Conventional practice in highway scheme evaluation has assumed that response is limited to route choice, and that there is no change in demand - the "fixed matrix" assumption. While accepting that other responses may occur, it has been argued in the past that there is little agreement about their magnitudes, while to model them could make scheme evaluation much more complex. In recent years this argument has been increasingly challenged. In the light of this, the Standing Advisory Committee on Trunk Road Assessment (SACTRA) has produced a report on generated (or "induced") traffic, defined as any combination of rescheduling existing trips to the peak, increasing frequency, decreasing occupancy, switching from other modes, changing destination, entirely new trips, and changes in land use. SACTRA suggests that, while in principle all these effects should be fully reflected in the modelling procedure, it may often be sufficient on the grounds of simplicity and practicality to use "simple elasticity methods". The work described in this paper was commissioned by the UK Department of Transport (HRTA Division) in the light of the SACTRA Report, to investigate what methods might be appropriate and in what circumstances, and their possible implications. A generalised model was designed and programmed to incorporate the following travel choices: changing time of travel, changing frequency, changing mode, changing destination. Three purposes were simulated, in order to deal with variation in sensitivity and differential incidence in terms of time of day and trip length: these were Commuting, Business and Other. A hypothetical study area was devised, loosely along the lines of the region between London and Birmingham, and the model was run with a set of changes in generalised cost broadly consistent with a major improvement in the main interurban network. The main aim of the project was to see whether the reactions predicted from the "full" model could be reasonably approximated by a simpler "elasticity" approach. (A) For the covering abstract see IRRD 880168.


  • English

Media Info

  • Features: References;
  • Pagination: p. 193-206

Subject/Index Terms

Filing Info

  • Accession Number: 00724208
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • ISBN: 0-86050-283-X
  • Files: ITRD
  • Created Date: Aug 19 1996 12:00AM