Slip Ramp Spacing Design for Truck Only Lanes Using Microscopic Simulation

For the Corridors of the Future project, slip ramps will provide access to trucks between the proposed truck-only lanes (TOLs) and general purpose lanes (GPLs) for trucks to exit using at-grade interchanges. This paper proposes recommendations for slip ramp spacing between the TOLs and the general GPLs along Missouri rural interstate highways using a microscopic simulation model, VISSIM. Simulation of peak period traffic conditions indicated that heavy vehicle speeds were directly proportional to the lengths of the merge, diverge, and link sections. The proposed design recommendations for slip ramp spacing are based on the results of these section lengths. Central composite design was used to generate the cases required for simulation. To ascertain the findings of the simulation study, Level-of-Service for the segments on GPL was determined. This paper provides practitioners and state Departments of Transportation with design recommendations for slip ramp spacing and lengths of merge, link, and diverge for the Corridors of the Future project.