Acceleration Ramps along High Operating Speed Roadways.

摘要

Until recently, guidelines for the geometric design of acceleration lanes used for the successful merge of an entering vehicle into a high-speed surface transportation system through-traffic lane have been based upon concepts and vehicle characteristics from the 1930s. Modern changes in vehicle characteristics and an increase in the percentage of large trucks using the roadway systems has necessitated reviewing the dated guidelines to determine if they are still suitable and if not, make recommendations for modifications. Consistency of use of the current guidelines has no doubt shaped driver behaviors over the years to promote expectations for desirable design features that encourage successful merging outcomes. This report summarizes the history of the geometric features of acceleration lanes, compares the outcome of recent merge-lane research studies, discusses prevalent driver behavior patterns from field studies and recommends the use of tapered and parallel type lanes in specific situations. Overall, the current AASHTO guidelines provide adequate acceleration lane length guidance values for all vehicles except heavy trucks. If a large percentage of heavy trucks are expected to use a particular merging lane, general planning guidelines are listed to accommodate their accelerating characteristics and provide adequate distance for an appropriate entering speed into the adjacent through traffic lane.