Rounding of Arrival and Departure Times in Travel Surveys: An Interpretation in Terms of Scheduled Activities

In travel surveys most respondents apply rounding of departure and arrival times to multiples of 5, 15 and 30 minutes: in the annual Dutch travel survey about 85-95 percent of all reported times are 'round' ones. We estimate rounding models for departure and arrival times. The model allows one to compute the probability that a reported arrival time m (say m=9: 15 am) means that the actual arrival time equals n (say m=9:21 am). Departure times appear to be rounded much more frequently than arrival times. An interpretation for this result is offered by distinguishing between scheduled and non-scheduled activities, and by addressing the role of transitory activities. We argue that explicitly addressing rounding of arrival and departure times will have at least three positive effects. 1. It leads to a considerably better treatment of variances of reported travel times. 2. It enables one to avoid biases in the computation of average transport times based on travel surveys. 3. It overcomes the problem that the use of travel survey data for the minute-per-minute records of the development of the number of persons in traffic displays erratic patterns.<BR><BR>