Potential Mode Shift from Transit to Single-Occupancy Vehicles on a High-Occupancy Toll Lane

Modifying a high-occupancy vehicle (HOV) lane to a high-occupancy toll (HOT) lane generally involves allowing single-occupancy vehicles (SOVs) to travel on the free-flow HOV lane for a toll. This may entice some transit riders to pay the toll to obtain the benefits of traveling in their own vehicle on the HOV lane. Thus, the introduction of a HOT lane has the potential to affect transit ridership negatively; this situation would lower the average vehicle occupancy (AVO) of the lane. To investigate this potential problem, surveys were distributed to park-and-ride bus passengers on two Houston, Texas, freeway corridors. Passengers’ responses to questions regarding their trip characteristics, their socioeconomic characteristics, and their stated preference scenarios were used to develop a mode choice model. Scenarios with varying tolls and travel time savings were simulated using this model. For all scenarios, only a small percentage of transit passengers would choose to switch to driving alone on the HOT lane. Transit passengers shifting to SOVs on the HOT lane would reduce average vehicle occupancy on the lane by only about 1% to 2%. SOV drivers shifting from the general purpose lanes to the HOT lanes are likely to affect AVO much more. However, as long as free-flow conditions are maintained, this analysis shows that the HOV lane can be successfully adapted to a HOT lane and move more people, even if a few transit passengers choose to drive alone.