STUDY OF OPERATIONAL CHARACTERISTICS OF LEFT-HAND ENTRANCE AND EXIT RAMPS ON URBAN FREEWAYS

THE PAPER IS ESSENTIALLY A COMPANION TO AN EARLIER REPORT DEALING WITH LEFT-HAND EXIT RAMPS FOR FREEWAYS AND IS DIVIDED INTO THREE MAIN SECTIONS' /A/ A STUDY OF THE GENERAL OPERATING CHARACTERISTICS OF LEFT- AND RIGHT-HAND ENTRANCE RAMPS ON URBAN FREEWAYS; /B/ AN ANALYSIS OF TRAFFIC BEHAVIOR ALONG A 2-MI SECTION OR URBAN FREEWAY CONTAINING TWO INTERNAL DIAMOND INTERCHANGES; AND /C/ A COMPARATIVE STUDY OF THE REPORTED ACCIDENT RATES AT A SAMPLE OF RIGHT- AND LEFT-HAND ENTRANCE AND EXIT RAMPS ON URBAN FREEWAYS IN THE CHICAGO AREA. BRIEF DESCRIPTIONS ARE GIVEN OF STUDY LOCATIONS AND STUDY TECHNIQUES, TOGETHER WITH A DISCUSSION OF MAJOR RESULTS. CONCLUSIONS DRAWN CONCERNING THE OPERATIONAL EFFICIENCY, RELATIVE SAFETY AND GENERAL SUITABILITY OF LEFT-HAND ENTRANCE AND EXIT RAMPS FOR URBAN FREEWAYS UNDER THE TYPE OF SITE CONDITIONS EXISTING IN THE CHICAGO AREA INCLUDE THE FOLLOWING' /1/ NONE OF THE LEFT-HAND RAMPS STUDIED CAUSED ANY PROLONGED DISRUPTION OF FLOW IN THE ADJACENT FREEWAY LANES, /2/ FLOW CONDITIONS ON A LEFT-HAND ENTRANCE FORMING PART OF AN INTERNAL DIAMOND INTERCHANGE WERE SIGNIFICANTLY DIFFERENT FROM THOSE ON A RIGHT HAND ENTRANCE CARRYING SIMILAR TRAFFIC VOLUMES AND FORMING PART OF AN EXTERNAL DIAMOND INTERCHANGE, /3/ EXTREMELY HIGH MERGING RATES WERE OBSERVED AT ONE LEFT-HAND ENTRANCE RAMP WITHOUT CAUSING AVERAGE LEFT LANE SPEEDS UPSTREAM TO FALL BELOW 45 MPH. SUPERSATURATED FLOW CONDITIONS RESULTED DOWNSTREAM. /4/ ON LEVEL SECTIONS OF HEAVILY TRAVELED URBAN FREEWAY IN THE CHICAGO AREA THE AVERAGE REPORTED ACCIDENT RATE PER MILLION RAMP VEHICLES WAS CONSISTENTLY HIGHER AT LEFT-HAND ENTRANCES AND EXITS THAN AT RIGHT-HAND ENTRANCES AND EXITS. NO SIGNIFICANT DIFFERENCE WAS FOUND IN THE AVERAGE SEVERITY OF ACCIDENTS AT LEFT AND RIGHT-HAND RAMPS. /5/ INDIVIDUAL DESIGN CHARACTERISTICS APPEARED TO HAVE A MORE SIGNIFICANT EFFECT ON THE ACCIDENT RATE AT A GIVEN RAMP THAN RAMP OR FREEWAY VOLUME ALONE, AND /6/ AVERAGE ACCIDENT RATES FOR BOTH LEFT AND RIGHT-HAND FACILITIES TENDED TO BE SLIGHTLY THOUGH NOT CONSISTENTLY HIGHER AT ENTRANCE RAMPS THAN AT EQUIVALENT EXIT RAMPS.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/hrr/1965/99/99-010.pdf
• 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.
• Authors:
  • Worral, R D
  • Drake, J S
  • Buhr, J H
  • SOLTMAN, T J
• Publication Date: 1965

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: pp 244-273
• Monograph Title: Freeway characteristics, operations and accidents
• Serial:
  • Highway Research Record
  • Issue Number: 99
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Crash rates; Crash severity; Diamond interchanges; Freeway operations; Freeways; Highway design; Interchange ramps; Ramps; Traffic crashes; Traffic flow; Urban areas
• Old TRIS Terms: Freeway design; Freeway entrances and exits; Freeway ramps; Freeway traffic accidents; Left side ramps
• Subject Areas: Design; Highways; Operations and Traffic Management;

Filing Info

• Accession Number: 00224769
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Feb 20 1994 12:00AM