Acceleration ramps along high operating speed roadways.
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2010-11-01
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Edition:Final report; Nov. 2010.
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Abstract: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.
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