MATHEMATICAL TECHNIQUES FOR ESTIMATION OF THE VALUE OF TRAVEL TIME SAVINGS: A REVIEW

A decrease in travel time is usually one of the benefits resulting from improvements to a transportation system. For cost benefit analysis of project proposals it is necessary to estimate the value of travel time savings. Methodologies which may be used for this purpose are reviewed with the aim of comparing the assumptions and limitations of the formulations and solution techniques used. The methodologies are divided into aggregate and disaggregate models. The aggregate models discussed are the gravity, entropy and abstract mode models. These are limited by their restricted behavioural basis and use of data describing zonal and inter- zonal characteristics. Any values produced by these models are calculated at the mean of the sample. The many disaggregate models are mostly based upon theories of individual decision making behaviour. The models are divided into simple, multinomial, general behavioural and functional measurement models. When applying any model the sources of error, aggregation of disaggregate results and the updating and transfer of results should be considered. Each of these issues and the precautions which may be taken, are discussed. The desirable properties of models for estimating the value of travel time savings are listed and used to compare the models reviewed. None of the models has all the properties, but functional measurement comes closest. For situations in which aggregate results are acceptable the elimination- by- aspects and satisfying models should be considered. (TRRL)