What Drives Decisions of Single-Occupant Travelers in High-Occupancy Vehicle Lanes?

High-occupancy toll (HOT) lanes are in operation, under construction, and planned in several major metropolitan areas. The premise behind HOT lanes is to allow single-occupant vehicles (SOVs) to access high-occupancy vehicle lanes (and a higher level of service) if they are willing to pay a toll. To maintain a high level of service in the HOT lanes, the toll rate is set dynamically to restrict the number of SOVs that access the facility lanes as they near capacity. Thus, HOT facilities provide operators of transportation systems with an additional tool: pricing. To use pricing effectively, it is critical for those operators to understand how drivers behave when faced with a set of traffic conditions and toll levels. This paper presents the results of an empirical investigation into the relationship between toll rate, traffic conditions, and SOV driver behavior, on the basis of data from the dynamically tolled I-394 HOT facility in Minneapolis, Minnesota. Analysis of the empirical data indicated that a large percentage of SOV drivers used the HOT lanes at different, yet predictable, rates throughout the morning peak period, even when there was no clear travel time advantage. After these users were accounted for, it was determined that the remaining SOV drivers used the HOT lanes at greater rates when the cost per hour of commute time saved was lowest. A model was developed that incorporates both of these findings, predicting HOT lane usage rates based on time savings, time of day, and toll rates, with an R² value of .684.