A crucial parameter when forecasting route choice in networks with road pricing is the assumed value of time for car drivers. This will determine the extent to which drivers are willing to take detours to avoid being charged. The purpose of this paper is to investigate this question using survey data from the Stockholm congestion charging trial. The estimation results in this study can be interpreted in two ways, depending on whether charging costs (at face value) of average marginal driving costs are taken as the relevant travel cost measure. Relative to charging costs, we obtain values of time of 174 kr/h for work trips and 190 kr/h for other trips, and values of distance of 2.19 kr/km for work trips and 2.40 kr/km for other trips. If we instead relate time and charging costs to average marginal driving cost, we get values of time of 127 kr/km for both work trips and other trips. Further, this interpretation means that expenditures for congestion charges are only worth 70% of driving costs. One possible interpretation of this is that 30% of the travellers in this group did not pay the charges out-of-pocket themselves, but had their costs covered by their employers. With either of the interpretations, drivers’ actual behaviour seem to imply considerably higher values of time for private cars than are typically used in traffic assignment modeling, usually obtained from stated preference studies or mode/destination choice models. This is the same conclusion reached by Lam and Small (2001) and Brownstone et al. (2003), analysing Californian value-priced highways. This could explain that the traffic diversion onto the non-priced bypass around Stockholm turned out to be less than forecasted.
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