United States Department of Transportation
i
Re-Evaluation of Ramp Design Speed Criteria: Review of Practice and Data Collection Plan
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1997-04-01
[PDF-3.10 MB]
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TRIS Online Accession Number:00900342
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Edition:Research Report (9/96-4/97)
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Abstract:Freeway ramp design speed criteria contained in current American Association of Highway and Transportation Official (AASHTO) and Texas Department of Transportation (TxDOT) design policies have been traced through roughly 50 years of technical literature. The evolution of design speed criteria has been documented and a technical rationale leading to periodic changes has been included. TxDOT ramp design speed criteria are, essentially, the AASHTO criteria. The origins of driver acceleration and deceleration rates, which are built into the AASHTO criteria, are experimental studies performed during the late thirties. Several studies have raised questions about the appropriateness of the AASHTO minimum allowable ramp design speed, which is 50 percent of the freeway design speed. Questions have also been raised about the adequacy of high-speed ramp lengths designed by AASHTO criteria. A Conceptual data collection plan has been designed to provide information that will answer questions regarding current criteria. Additionally, a nationwide survey of ramp design agencies indicates that 1) there is a variety of different design policies, 2) most designers have concern for entrance ramps, as opposed to exits, and 3) safety is the most commonly used evaluation measure.
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