Our point of departure is the finding of large differences between modes in the value of travel time (VTT) found from a stated choice experiment involving travel time and cost with more than 6000 respondents. From a series of within-mode experiments for the current mode of respondents, the VTT for car drivers was found to be several times larger than the value for bus passengers, while the value for train passengers is in between. Such results give cause for concern but are not unique. The differences could not be explained by differences in income and comfort. Two competing explanations are advanced for the observed differences: strategic behaviour and self-selection. The self-selection story is convenient, since it indicates that preferences are in fact being measured and hence VTT is being measured.The strategic behaviour story is very inconvenient, since it implies thatthe data do not reveal preferences. The study aims to provide empirical evidence to discern between these two competing explanations. Under strategic behaviour, respondents think outside the context of the experiment and consider their ability to influence political decisions. For car there is no established mechanism whereby respondents could actually pay for reduced travel times. Respondents may therefore feel that it will cost them nothing to express a wish to pay for increased speed. Conversely, public transport passengers pay fares set by political decision while travel times maybe deemed difficult to change as they are determined by traffic conditions and not politically. Passengers may hope that expressing a low willingness to pay may influence the setting of fares. In both cases, choices cannot be seen as an expression of preferences. Those with high VTT may choose the fast modes, car and then train. Those with low VTT tend to choose slowmodes. So the differences in VTT that are seen may be due to self-selection. In the study, respondents are interviewed to identify a recent trip. They then carry out a within-mode stated choice exercise for this trip in the current mode. This is where large differences are found between modes mentioned above. Respondents are then asked to identify an alternative modefor their current trip and a similar experiment is carried out within this alternative mode. Under the self-selection hypothesis it is expected respondents carry their unobserved VTT with them to the alternative mode. It is expected that current car drivers to have a high VTT also in bus as an alternative and conversely for bus passengers. On the other hand, if responses are strategic, there would be a large decrease in the VTT of car drivers as they go to bus and the converse for bus passengers. The data thus allow an empirical test of the two competing hypotheses. After controlling for the choice of mode it is found that self-selection into modes explainsmost of the observed differences. Expectations concerning comfort are also present as current car drivers have larger VTT in train and current train users have lower VTT in car. For the covering abstract see ITRD E137145.
Samenvatting