TRAFFIC BEHAVIOR AND OFF-RAMP DESIGN
OFF-RAMP TERMINALS ON CALIFORNIA FREEWAYS ARE DESIGNED ACCORDING TO THE DIRECT ANGULAR TAKE-OFF PRINCIPLE, AS CONTRASTED WITH THE PARALLEL DECELERATION LANE PRINCIPLE. THE SHAPE OF THE DIRECT TYPE OF OFF-RAMP AS IT LEAVES THE FREEWAY IS CONSIDERED GENERALLY SATISFACTORY, BUT THE DAMAGE TO GUARDRAILS AND MARKERS, THE TIRE SCUFFS ON CURBS, AND SOME REPORTED ACCIDENTS INDICATE THAT THE DECELERATION DISTANCE TO THE RAMP CURVE BEYOND THE CURB NOSE MAY BE INADEQUATE. THIS STUDY WAS MADE TO OBTAIN FACTUAL DATA ON THE OPERATING CHARACTERISTICS OF THE TRAFFIC AS IT LEAVES THE FREEWAY ON VARIOUS EXISTING OFF-RAMPS. IT WAS DESIRED TO DETERMINE WHETHER THE LENGTH OF THE RAMP TANGENT APPROACHING THE RAMP CURVE HAS ANY EFFECT ON RAMP SPEED, AND IF IT DOES WHAT THE OPTIMUM LENGTH OF SUCH A TANGENT SHOULD BE. THE SPEED OF VEHICLES USING THE DECELERATION LANE WAS DETERMINED BY 3 FACTORS IN COMBINATION' /1/ THE SPEED OF VEHICLES IN THE OUTSIDE LANE OF THE FREEWAY, WHICH INFLUENCES THE EXIT SPEED, /2/ THE LENGTH OF TANGENT AVAILABLE TO DECELERATE, AND /3/ THE RAMP CURVE OR TERMINAL WHICH DETERMINES THE SPEED TO WHICH THE RAMP TRAFFIC MUST DECELERATE. THE IDEAL OFF-RAMP DESIGN IS THE ARRANGEMENT OF THE DIVERGING AREA TO PROVIDE THE LEAST INTERFERENCE TO THROUGH TRAFFIC AND A LENGTH OF TANGENT TO ENCOURAGE HIGH-SPEED EXIT. FROM DATA OBTAINED, IT IS SEEN THAT THE LENGTH OF TANGENT FROM THE 12-FT POINT SHOULD BE AT LEAST 450 FT WHEN THE RAMP CURVE HAS A RADIUS OF 400 FT.
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Supplemental Notes:
- Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
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Authors:
- Fukutome, Ichiro
- Moskowitz, Karl
- Publication Date: 1963
Media Info
- Media Type: Print
- Features: Figures; Tables;
- Pagination: pp 17-31
- Monograph Title: Freeway operations
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Serial:
- Highway Research Record
- Issue Number: 21
- Publisher: Highway Research Board
Subject/Index Terms
- TRT Terms: Curves (Geometry); Data collection; Deceleration; Deceleration lanes; Design; Freeways; Highway operations; Intersection elements; Length; Off ramps; Ramps; Speed; Tangents; Traffic; Vehicles
- Geographic Terms: California
- Old TRIS Terms: Direct angular take-off
- Subject Areas: Design; Highways; Operations and Traffic Management; Vehicles and Equipment;
Filing Info
- Accession Number: 00224745
- Record Type: Publication
- Files: TRIS, TRB
- Created Date: Dec 12 1994 12:00AM