The reassignment of time from one activity to another is a subject which has been explored for more than 30 years by researchers from many different perspectives, including those with an interest in either the study of the labour market, the analysis of home activities, or the understanding of travel behaviour. The theories of time allocation deal with the issue of time valuation in many different ways. From these, many concepts of value of time emerge, depending on how a period of time is looked at: as a valuable resource, as something to be reassigned, or as something to be reduced. These concepts are clearly identified, and their evolution in the literature is presented. The subjective value of travel time (SVTT) is the amount the individual is willing to pay in order to reduce by one unit his or her travel time. The simplest manifestation of this is the choice between fast expensive modes and cheap slow ones. The usual procedure to measure SVTT is to estimate discrete travel-choice models and to calculate the rate of substitution between time and money from the estimated utility function. The interpretation of this ratio depends on the underlying theory that generates such utility. The authors show the relation between the SVTT and the different elements in the theory, starting with the goods-leisure framework, expanding it to all activities and to the consideration of aggregate relations between consumption and leisure. The elements to understand and to calculate social prices of travel-time savings (SPT) to be used in (social) project appraisal are given. The final section includes a synthesis and conclusions.
Abstract