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The Importance of Considering Spatial Variation in Trip Rates and Public Transport Accessibility in Conventional Trip End Modelling

UK’s National Trip End Model (NTEM) includes a series of models that forecast trip productions and attractions by Middle Layer Super Output Area (MSOA); these are widely known as trip ends and can be categorised by mode, trip purpose, car ownership level, and time period. NTEM is one of the main national datasets in the UK, owned and maintained by Department for Transport (DfT) and widely used within the industry for trip generation modelling and forecasting, intended to provide consistency across various transport studies at spatially aggregate level. One of the main weaknesses of NTEM estimates is uncertainty in estimated trip ends when used to provide an estimate of absolute travel demand at a spatially disaggregate level (e.g. for the purpose of synthetic matrix development or building absolute demand models). For example, Transport Appraisal Guidance (TAG) Unit M2.2 (base year matrix development) states that “… estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments”. This uncertainty is mainly due to the following two reasons: - lacking representation of spatial variation in trip rates underpinning trip end estimates; and - missing the link between mobility and accessibility. Whilst this is widely known, there is limited quantified evidence on the range of errors associated with NTEM trip ends at various spatial levels and demand segments; it is the aim of this study to establish this missing evidence and provide further recommendations on how existing NTEM estimates should be used and how these limitations can be addressed. In particular, the following specific objectives are met in this study: - to quantify the spatial variation in trip rates and the difference between underlying trip rates in NTEM and local trip rates; - to quantify the impact of public transport accessibility on trip rates; - to develop a bespoke trip end model, based on NTEM, to reflect spatial variation in trip rates and the link between mobility and accessibility. National Travel Survey (NTS) is used to estimate local trip rates at various spatial levels across the UK, including trip rates for the 8 NTEM area types, used to estimate NTEM trip ends. Analysis of Variance (ANOVA) techniques will be used to examine if variation of trip rates between main urban areas within NTEM area types is significant. The results are used to quantify the expected errors in NTEM trip ends when they are used at county and local authority district level; this informs the suitability of NTEM trip end estimates at these spatial levels. AECOM has used Negative Binomial regression models to estimate trip rates underlying current NTEM for the DfT (DfT, 2016). Similar models will be used and developed further to quantify the partial effect of public transport accessibility on trip rates, when other contributing factors are controlled for through inclusion of relevant variables in the model. The results are used to estimate the error in NTEM trip ends resulting from the missing link between trip rates and accessibility. AECOM has recently developed the Pan Regional Transport Model (PRTM) for Leicestershire County Council to help inform projects that the authority is undertaking. In addition to a trip end model, the PRTM consists of a highway model, a public transport model, a demand and parking model and a land-use model. The existing trip end model within the PRTM, which is based on NTEM, is updated to include the spatial variation in trip rates that are established, and the link between public transport accessibility and trip rates. The comparison of trip ends from the existing and updated trip end models at various spatial levels is indicative of the additional accuracy introduced by considering these refinements to the PRTM trip end model.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Bibliography; Figures; Tables;
  • Pagination: 17p
  • Monograph Title: European Transport Conference 2020

Subject/Index Terms

Filing Info

  • Accession Number: 01766009
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 25 2021 10:12AM