Many different variables affect car ownership, demand, distribution, mode choice and route choice of transport. The core variable, however, is travel time, hence the importance of values of time. Accordingly, a thorough understanding of it is fundamental in order to be able to model the traffic and environmental effects of different policy instruments regarding transport.
One of the issues is the estimation of value of time for different time components (e.g. waiting time versus driving time).
A better knowledge of value of time is one of the core aspects concerning improvements of operational, tactical and strategic transport models, since time is the core explanatory variable concerning travel behaviour.
The project focuses on:
- methodological development of models and estimation techniques concerning value of time distributions and non-linear value of time in traffic models;
- empirical tests and evidence on the proposed methods;
- development of methods to transfer value of time components from traffic models to socio-economic appraisal methods.
One of the important issues in the project is to better understand, measure and model the role of socio-economic variables against random variables in describing the distribution of values of time. This includes income variation as a core variable, as well as other variables. The elements of sign and magnitude of time savings relative to the present situation are also investigated concerning methods for model estimation.
Initially, the theoretical framework is developed. After that, a major data collection is carried out by undertaking interviews with travellers using RP and SP techniques (Revealed Preference and Stated Preference). Large amounts of existing data from several Danish traffic models and investigations are also used.
The project has been concentrated on the empirical parts. In particular, it has focused on whether the so-called mixed-logit models can be used to evaluate the distribution of values of time within a certain part of the population. It has been proved that the frequently used assumption of constant value of time is rarely true.
Furthermore, methods have been developed to clarify the empirical distribution of values of time, as well as methods to calculate distribution, median and variance thereof. The usual method, just taking the average of the distribution of the single coefficients, has been proved to be incorrect.
The results of the projet have been used in an initial project to a national project of time values.