Abstract: Current freeway entry ramp design speed criteria were evaluated through observations of twenty ramps in four Texas cities. Field observations of ramp and freeway traffic speed-distance relationships were made using videotaping methods. Traffic operations were described in terms of ramp and freeway right-lane speeds and accelerations, as well as ramp driver merging locations, accepted time gap sizes, and freeway time headways. The researchers determined that observed ramp driver acceleration rates and AASHTO values were comparable. For virtually all observations, ramp driver speeds are found to be greater than 50% of the freeway design speed, leading to a recommendation that the design policy provision allowing ramp design speeds to be as small as 50% of the freeway design speed be deleted. The ability of entry ramp drivers to see, prior to reaching the ramp gore, freeway right-lane traffic, into which merging is intended, was found to be very important. This finding led to a recommendation that the AASHTO acceleration lane should be considered to begin only when ramp drivers have an unobstructed view of freeway right-lane traffic.
Publication Year: 1999
Publication Date: 1999-12-01
Language: en
Type: article
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Cited By Count: 5
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