Influence of vehicle occupancy on the valuation of car driver's travel time savings: Identifying important behavioural segments

Studies that develop estimates of the value of travel time savings (VTTS) for car travel typically assume that the VTTS of the driver is the only relevant measure of the worth of time savings. Although there is a recognition that the presence of passenger's may condition the driver's choice of route and VTTS, the evidence is somewhat limited on the impact that the number of passengers has on the driver's VTTS. This is especially problematic when evaluating the role that policy instruments such as HOV lanes might play in delivering travel time savings for a specific occupancy, as well as the growing opportunities to have differentiated congestion charges and tolls according to occupancy. This paper investigates the role that the presence of the passenger plays in the VTTS of the non-commuting car driver. We find that the overall mean VTTS varies across the number of passengers (from $19.99 to $13.22 per person hour), declining as the number of passengers increases; however this is largely attributable to the decreasing mean VTTS for slowed down time in contrast to a 'flat' mean free flow time. The implications on travel time benefits ignored (through simple averaging) in previous studies, especially tollroad studies, and hence the impact on infrastructure justification, is potentially profound, given the important role played by VTTS and its variation over the number of passengers.