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Research Questions

  1. What is the current evidence base on diversion factors, bus fare and generalised journey time elasticities?
  2. Given the evidence base, how should the values currently recommended by the UK Department for Transport for these factors and elasticities be updated?

This study uses a rapid-evidence review process to identify evidence on bus fare and journey time elasticities and diversion factors for all modes (diversion factors quantify the impact of changes on one mode on the demand for other modes and for new trips). It uses a systematic search procedure to identify relevant academic and grey literature through structured database searches, as well as making enquiries to experts in the field to identify material, such as unpublished studies. The study focuses on material produced in or that is relevant to the UK. Little recent evidence on bus fare elasticities (in the UK) — and little evidence on bus journey time elasticities generally — was identified in the systematic search process. However, a substantial database of diversion-factor evidence was identified and collated. Recommendations are provided, based on analysis of the available evidence. In general, we find that the evidence on diversion factors is very diverse, covering a wide range of mainly metropolitan geographies, trip purposes, journey types and alternative transport options.

Key Findings

Diversion factors have been derived from a substantial, but diverse, database.

  • A revised set of recommended diversion factors are presented for interventions on bus, car, rail, light rail/metro, cycle and walk. Further, best-estimate values for a number of scenarios that are considered to be useful for transport appraisal purposes are provided.

Very little new evidence on bus fare elasticities has been identified in the review.

  • We do not recommend any changes to the overall range of values for bus fare elasticities. However, based on the additional evidence from Wardman (2014), recommended values for area type and trip-purpose segmentations are presented.

We have uncovered very little new evidence on bus journey time elasticities.

  • We find that there is very little evidence on bus in-vehicle time (IVT) or generalised journey time (GJT) elasticities. We are not aware of any studies that determine GJT elasticities directly and the recommended values are derived from IVT elasticities.

Recommendation

  • More and better evidence on diversion factors should be collected.

Research conducted by

The research described in this report was prepared for the UK Department for Transport (DfT) and conducted by RAND Europe and SYSTRA.

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