Alternative strategies to estimating large-scale travel demand models: the U.K. national travel model

This paper will compare two different strategies that have been used to estimate the mode/destination demand model component of the U.K. National Transport Model (NTM). One strategy has been based on adjusting an aggregate a-priori model designed to reproduce aggregate elastistities, to match observed aggregate travel demand from a national survey. The other has beento analyse the travel survey at a disaggregate level, retaining the possibility of adjusting parameters should implied elasticities appear indefensible. The first part of the paper briefly describes various national travel models and outline some similarities and differences with the NTM. The paper highlights the most interesting features of the NTM and ends with a section on how lessons learned from this re-estimation effort can be used to inform other comparable national transport models. One key characteristic of the NTM is that it operates in two zonal systems a more detailed zonesystem for highway and transit assignments and a more aggregate zone system, the level at which the mode/destination demand model operates. This two-level system is imposed to a certain extent by the characteristics of the National Travel Survey (NTS), which is the primary data source for the demand component of the NTM. While more disaggregate information is available from the NTS, confidentiality requirements lead to certain restrictionsbeing imposed on the release of this data. The modelling techniques used to overcome these particular data restrictions are discussed. Given that many countries have limited data collection at the national level, or this information is restricted in various ways, there are clearly lessons to belearned from the NTM about modelling in a data-restricted environment. Another important feature is that NTM was re-estimated with one eye towards testing certain policy measures, such as road pricing. Details are provided on how the models were designed to incorporate such policy tests, including how decisions were taken on the trade-offs between different features,including allowing an appropriate sensitivity to policy changes, ensuringthe implied values of time were within acceptable ranges and model run time. While the details of the NTM are specific to the UK. context, developing any national transport model will inevitably require taking decisions on which policies should be tested and which aspects of the model are most critical if different features come into conflict. Thus, the lessons learned from re-estimating the U.K. National Transport Model can be used by other practitioners developing their own national models in other national contexts. For the covering abstract see ITRD E137145.

  • Authors:
    • GUNN, H
  • Publication Date: 2007


  • English

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  • Accession Number: 01100018
  • Record Type: Publication
  • Source Agency: TRL
  • Files: ITRD
  • Created Date: May 27 2008 9:26AM