Modeling Intertrip Time Intervals between Individuals’ Overnight Long-Distance Trips

Long-distance and overnight travel are growing in importance in the United States, yet the data and methods needed to model these activity patterns are lacking. One important factor for activity simulation is the interval between overnight trips away from home. This study used a unique 1-year panel data set of overnight trips for the estimation of a negative binomial regression model of intertrip time intervals. Most respondents indicated that they took between two and seven overnight trips per year, but time between trips varied widely regardless of the total number of trips. This time difference suggests some clustering of trips for some but not all people. Model results indicated that both regional and household attributes affected intertrip time intervals, but that both prior and next trip factors were significant. The distance from home on previous trips and income were not factors in intertrip interval times. The results of this study demonstrate the range of factors needed to model the time interval between trips. The model format lends itself well to activity simulation models that can expand beyond 1 day and the local region to include 1 year of travel and, potentially, a global landscape. In this way, long-distance and overnight travel can be integrated more appropriately into transportation system planning.