A corridor-based methodology for the design of open access high occupancy toll lane facilities

Open access High Occupancy Toll (HOT) lane facilities allow vehicles to move freely into and out of the managed lane at any point along a corridor, permitting significant mobility from entrance and exit ramps. However, a potential safety concern exists when the mainline and HOT lanes are behaving differently. In certain circumstances, the general purpose lane adjacent to the HOT may be broken down while the HOT itself continues to operate at high speed (due to its managed nature). Vehicles seeking to enter the HOT must negotiate a potentially large (35 mile per hour or more) speed differential. As those vehicles enter the HOT, they must select a sufficiently large gap and accelerate to speed. Subsequent vehicles in the HOT may have to decelerate in order to avoid a collision, forming a shockwave in the HOT lane. This methodology models the formation of those shockwaves for varying conditions on the HOT and adjacent general purpose lane. Realistic traffic streams are reproduced for the HOT using measured parameters for headway and platoon formation and vehicles from the general purpose lane are introduced at varying low speeds. By iterating through this procedure many times, the distribution of shockwave lengths for any given conditions can be produced. The target conditions for modeling include 15 to 42 vehicles per mile on the HOT lane with vehicles being introduced with speeds between 10 and 45 miles per hour. These ranges were selected to cover conditions where the HOT has not broken down to a congested state while the general purpose lanes have. Analyzing historical data for a corridor allows the shockwave length distributions to be combined into comprehensive considerations of shockwave distributions for any given location within a corridor. Each of these comprehensive shockwave distributions represents the overall behavior of the location over time. These can then be used to assess the safety of the corridor and provide guidance on regions within an HOT corridor which may require lane-changing prohibitions to improve safety.