Assessment of the Value of Travel Time from Stated Choice Surveys - the Treatment of Lexicographic Answering
E J van de Kaa, TRAIL Research School, NL
This paper compares two Dutch VOT surveys. It shows that strong lexicographic answers should be included in the analysis and demonstrates that the commonly followed MNL analyses underestimate VOT.
Stated choice surveys have been used in many countries all over the world as an important tool to assess the Value Of Travel time. Such surveys generally collect information about the travel behaviour as well as about a recently experienced trip and socio-economic characteristics of the respondents. The core of the survey questionnaires consists of a series of choice sets in which the alternatives are characterized by at least two attributes, i.e. trip duration and monetary cost, mostly compared to those of some recently experienced reference trip.
The value of travel time is commonly assessed by analysing all answers independently, with a multinomial logit model based on the premises of Random Utility Maximization theory. Many travel behaviour analysts found that a considerable share of the respondents to such stated choice surveys systematically selected those alternatives with the ?best score? on one attribute only. Their opinions differ on how to cope with this so-called ?strong lexicographic answering'.
This paper compares the individual responses to the 1988 and 1997 Dutch national Value Of Travel time surveys following the premises of Extended Prospect theory. This implies that the choice/answering sequences of the individual respondents rather than their separate answers are treated as the basic unit of analysis, and presumes the co-occurrence of survey population segments that apply different choice behaviour strategies and different attribute valuation approaches.
The paper demonstrates that the strong lexicographic answers should better be included in the analysis. It also shows that the commonly followed MNL analyses of individual choice decisions underestimate the value of travel time compared to an approach that presumes intrapersonal consistency in the answering of the stated choice questions.
Keywords: Value of travel time; Stated choice survey; Prospect theory; Lexicographic decision rule.
Association for European Transport