Modeling the Rounding of Departure Times in Travel Surveys: Comparing the Effect of Trip Purposes and Travel Modes

Abstract

Rounding errors are often observed in reported trip departure and arrival times in paper-based travel surveys, and most of the reported times are multiples of 5, 15, 30, or 60 min. However, the rounding is rarely systematically analyzed. This study aimed to analyze the rounding of reported departure time in paper-based travel surveys by extending the rounding model proposed by Rietveld in 2002. The model parameters were estimated using the maximum likelihood method with constraints. The data in a 2012 household travel survey in Kumamoto, Japan, was used. The data in Japan were found to be often rounded to 10 min, which contrasted with the frequent rounding to 15 min in the Netherlands and United States. The model estimation results indicated that rounding to 5 and 10 min most often occurred. The response-error distribution when the reported departure time was 30 min was demonstrated using the Bayesian theorem and it was shown that the probabilities in which the actual departure times were exactly 30 min, 25–35 min, and 20–40 min were 7.9%, 63.5%, and 84.3%, respectively. Business trips were found to contain large rounding errors, and most public-transportation trips exhibited smaller rounding errors. These results may be used to refine several travel behavioral models in the future.