Hess, S., Bierlaire, M. and Polak, J.W. (2005) Estimation of value of travel-time savings using mixed logit models. Transportation Research Part A: Policy and Practice, 39 (2-3). pp. 221-236. ISSN 0965-8564Full text available as:
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In this paper, we discuss some of the issues that arise with the computation of the implied value of travel-time savings in the case of discrete choice models allowing for random taste heterogeneity. We specifically look at the case of models producing a non-zero probability of positive travel-time coefficients, and discuss the consistency of such estimates with theories of rational economic behaviour. We then describe how the presence of unobserved travel-experience attributes or conjoint activities can bias the estimation of the travel-time coefficient, and can lead to false conclusions with regards to the existence of negative valuations of travel-time savings. We note that while it is important not to interpret such estimates as travel-time coefficients per se, it is nevertheless similarly important to allow such effects to manifest themselves; as such, the use of distributions with fixed bounds is inappropriate. On the other hand, the use of unbounded distributions can lead to further problems, as their shape (especially in the case of symmetrical distributions) can falsely imply the presence of positive estimates. We note that a preferable solution is to use bounded distributions where the bounds are estimated from the data during model calibration. This allows for the effects of data impurities or model misspecifications to manifest themselves, while reducing the risk of bias as a result of the shape of the distribution. To conclude, a brief application is conducted to support the theoretical claims made in the paper.
|Copyright, Publisher and Additional Information:||Copyright © 2004 Elsevier Ltd. This is an author produced version of a paper published in 'Transportation Research Part A: Policy and Practice.' Uploaded in accordance with the publisher's self-archiving policy.|
|Keywords:||estimation, mixed, logit, models, travel time, savings|
|Institution:||The University of Leeds|
|Academic Units:||The University of Leeds > Faculty of Environment (Leeds) > Institute for Transport Studies (Leeds)|
|Depositing User:||Mrs Cassie L. Dupras|
|Date Deposited:||02 Apr 2009 15:35|
|Last Modified:||09 Jun 2014 06:53|