Managed Lane Ramp and Roadway Design Issues (0-4160-10)

Texas is exploring the use of managed lanes in congested urban corridors. This report discusses the findings from an evaluation of managed lane ramp design issues. Most of the recent literature regarding ramp design has focused on ramp design speed and truck performance. To have an appreciation for current department of transportation practices, a search of each state's design manual was conducted via the Internet. Of the 23 states that had all or part of their design manuals online, 12 had some material available concerning the design of ramps. The potential managed lane system in Texas could contain elements of systems that are currently in use in other communities. As part of this research project, members of the research team visited the New Jersey Turnpike. Simulation was used to obtain an appreciation of the effects on corridor operations when several pairs of ramps are modeled. Speed was the primary measure of effectiveness used to evaluate the effects of different ramp spacings, volume levels, and weaving percentages. The research found that a direct connect ramp between a generator and the managed lane facility should be considered when 400 veh/hr is anticipated to access the managed lanes. If a more conservative approach to preserving freeway performance is desired, then a direct connect ramp should be considered at 275 veh/hr (which reflects the value when the lowest speeds on the simulated corridor for the scenarios examined were at 45 mph or less).