Symmetry, Aggregation, and the Practical Specification of Travel Choice Models

This paper will discuss a fundamental issue in establishing the validity of travel choice models for economic appraisal is whether or not they adhere to the so-called “integrability” conditions. These conditions ensure that an underlying utility function from which demand can be derived exists. Conventionally, these integrability conditions exploit “continuous” demand theory, wherein preferences are defined on a continuous commodity or attribute space. Travel choice models may be seen as special case of continuous demand theory, such that choice is restricted to a finite and exhaustive subset of the commodity/attribute space, and this provokes some challenges in translating the integrability conditions. The purpose of this paper is to articulate the manner in which the aforementioned symmetry of substitution applies to travel choice models, and the implications that follow for the practical specification of such models. To this end, the authors consider two alternative representations of the discrete-continuous interface, as follows. First, the authors consider a problem of joint discrete-continuous demand, such that the demand for continuous consumption is conditional on the discrete choice. An example of this problem would be where a household makes a discrete choice of whether to purchase a particular car (whether as an additional or replacement car), and contingent on the discrete choice decides the quantity of mileage that will be ‘consumed’. Second, the authors conceptualize discrete choice as an end in itself, such that the demand for the ‘continuous’ consumption might simply be seen as the sample enumeration of discrete choices. An example of this problem would be where a commuter chooses the mode by which he/she will travel to work, and the total number of commuting trips (say over the course of a year) is readily predictable. The analysis presented in this paper reveals a clear message for practice, and one that must be heeded if the validity of economic appraisals from discrete choice models is to be defended.

• Record URL:
  https://aetransport.org/past-etc-papers/conference-papers-pre-2009/conference-papers-2009
• Corporate Authors:

  Association for European Transport (AET)

  1 Vernon Mews, Vernon Street, West Kensington
  London W14 0RL,    
• Authors:
  • Batley, Richard
  • Ibánez, J N
• Conference:
  • European Transport Conference, 2009
  • Location: Leiden Leeuwenhorst Conference Centre , Netherlands
  • Date: 2009-10-5 to 2009-10-7
• Publication Date: 2009

Language

• English

Media Info

• Media Type: Web
• Pagination: v.p.
• Monograph Title: European Transport Conference, 2009 Proceedings

Subject/Index Terms

• TRT Terms: Appraisals; Choice models; Cluster analysis; Demand; Discrete systems; Economic factors; Mode choice; Public transit
• Subject Areas: Highways; Planning and Forecasting; Public Transportation; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 01345438
• Record Type: Publication
• Files: TRIS
• Created Date: Jul 21 2011 3:08PM