Abstract

Knowing what people think about the usefulness, fairness, and success of new transport initiatives is vital information for planners and project evaluators. Methods for studying the complex relationships between attitudes and choice behaviour need to be included in evaluation processes. 

The attitudes of an individual faced with a new transport option will depend in part on whether the individual can take advantage of the new option, whether he or she actually chooses to take advantage, and the perceived benefits of the option, to the individual and to the community. Transport planners use choice models to understand factors affecting demand, but modelling of attitudes has not received similar attention. In this paper we demonstrate how a joint model of attitudes and behaviour can be used in comprehensive project evaluation. The approach involves analysing attitude survey data using a structural equations model designed for use with discrete choice and ordinal-scale variables. 

Our application involves the evaluation of responses to a project that allows solo drivers to pay a fee to use a carpool, or high-occupancy vehicle (HOV) lane facility on the Interstate 15 (1-15) Freeway in San Diego. The attitude survey is of subscribers to the program and a random sample of other freeway users. Four endogenous variables are explained as functions of each other and of exogenous variables such as income, household composition, age and gender. These endogenous variables are: (1) choice of subscription to the program, (2) mode choice of carpooling versus solo driving, (3) perception of the seriousness of the traffic congestion on the route, and (4) attitude towards allowing solo drivers to pay to save time by using the carpool lanes.

Abstract

This paper is a case study of carpooling behavior on the 91 Express Lanes. The 91 Express Lanes are the nation’s first implementation of High Occupancy/Toll (HOT) lanes where carpools with three or more passengers could use the lanes for free (at the time the data for this study was collected) and others pay a toll that varies by time of day to use the premium Express Lane. One concern over such a policy is that people won’t carpool if they can just pay for the travel time savings that they would normally obtain by carpooling and using a High Occupancy Vehicle (HOV) lane. Our survey data show that the rate of carpooling did not change much between the opening of the Express Lanes and now, there is a lot of changing between modes (increases and decreases in the number of passengers), there are a large number of people that carpool a few times a week, and that HOV-2s use both the regular lanes and the Express Lanes. We further investigate whether HOT lanes encourage carpooling by modeling carpool formation with discrete choice models. The results show that mode choice behavior in the corridor is similar to carpooling behavior in other locations and carpooling in the corridor is not discouraged.