A Study on Lane Operation Restriction (LOR) Policy at On-ramp Junctions

Abstract

Abstract On-ramp junctions on freeways are subject to vehicle merging interactions between main travel lanes and ramp flows. The turbulence created by these interactions often causes congestion, and can lead to breakdown when the combined volume from the ramp and the mainline exceed the capacity of the downstream freeway segment. This study discusses a potential application for freeway control policy at the ramp junction – the Lane Operation Restriction (LOR) policy. This policy would provide particular attention to traffic operation improvements at on-ramp junctions with relatively high flow rates from the ramp. Principles of LOR policy would be based on empirical data and analysis findings. The empirical data are analyzed upstream and downstream of on-ramp junctions on six-lane freeways using a database for the National Cooperative Highway Research Program (NCHRP) 3- 37. It was observed that lanes 2 (middle lane) and 3 (median side lane) show a higher density-speed relationship than the shoulder lane upstream of the junctions. In addition, the breakdown condition and congestion spread across all freeway travel lanes when the flow of lane 1 (shoulder side lane) is suddenly increased to near capacity at the ramp influence areas. A simulation analysis employing the LOR policy is introduced evaluating the ramp junction influence areas, its downstream and upstream areas. It concludes that traffic operations in the vicinity of on-ramp junctions can be significantly improved when upstream vehicles are guided to shift from lane 1 to lanes 2 and 3 before arriving at on-ramp junctions and restraint lane changes at the ramp influence area.