TRAVELLERS RESPONSE TO UNCERTAINTY: THE PARTICULAR CASE OF DRIVERS' RESPONSE TO IMPRECISELY KNOWN TOLLS AND CHARGES

Abstract

This paper builds and expands an aspect of the paper by Bonsall et al. (Experiments to Determine Driver Response to Different Forms of Road Pricing) which attracted considerable interest at the 1998 European Transport Conference (see ITRD E103862). The main sources of data for this analysis were questionnaire surveys conducted in 1997 and 1998 among city centre car park users. The questionnaires sought respondents' attitudes to road charges and posed stated preference questions to investigate how route choice might be influenced by different levels of charge and by the degree of certainty with which the charge was known. The analysis of the respondents' route choices showed a strong aversion to charges whose precise value is not known in advance but, contrary to expectation, it was noted that the strength of this aversion was reduced when the degree of uncertainty was at its maximum. This latter result reflected earlier findings which had suggested that, despite expressing a particular dislike for charges whose magnitude was not known in advance, drivers' route choices indicated a stronger aversion to charges which were precisely known. The effect was explored via segmented tabulation and modelling and was found to vary with the respondents' income and gender. Possible explanations of the effect, which is clearly inconsistent with Expected Utility Theory, are explored and discussed. Although some explanation is found in the tenets of Khaneman and Tversky's Prospect Theory, it is concluded that the most satisfactory explanation is a tendency, particularly, among male drivers and those with a relatively low income, to begin gambling when faced with a series of uncertain outcomes. A final discussion explores the implications of these results, and on their explanation, for the design of questionnaires and for the prediction of driver response to imprecisely known road charges and other uncertain phenomena such as uncertain travel times. For the covering abstract see ITRD E105584.