Travel time variability

Increasing traffic leads to increasing severity, spatial extension and duration of congestion. Congestion has two immediate consequences. One is that travel times increase on average. Another is that travel times become increasingly variable and unpredictable. When performing economic appraisal of transport policies it is important to account for both. This is fast becoming widely acknowledged in many countries around the world. The subject is, however, quite difficult for several reasons and so far there is no established consensus on how to define and value travel time variability. This report was commissioned by the Danish Ministry of Transport and its agencies Vejdirektoratet (the Road Directorate) and Trafikstyrelsen (the Rail Agency). Its purpose is to establish a definition of travel time variability and its value that is theoretically sound, possible to estimate from individual preferences, and applicable with existing or realistically foreseeable traffic models. In addition, the report provides short term recommenda- tions for including valuation of travel time variability in Danish practice for economic appraisal of transport projects and outlines a future Danish study of the valuation of travel time variability.