TRAFFIC CONTROL & ROADWAY ELEMENTS - THEIR RELATIONSHIP TO HIGHWAY SAFETY/REVISED. CHAPTER 12 ALINEMENT

THE CURRENT STATE OF KNOWLEDGE CONCERNING HORIZONTAL AND VERTICAL ALIGNMENT, THEIR COORDINATION, AND THE USE OF TRAFFIC CONTROL DEVICES IN ASSISTING DRIVERS TO ANTICIPATE ALIGNMENT CHANGES IS REVIEWED AND DISCUSSED. MOST STUDIES HAVE CONCLUDED THAT CURVATURE IS STRONGLY RELATED TO ACCIDENTS WITH SIGNIFICANT INCREASES IN ACCIDENTS FOR CURVATURE OVER 8 DEG. IN ADDITION, THERE IS EVIDENCE THAT CURVE FREQUENCY IS A CRITICAL FACTOR, IN THAT THE INTRODUCTION OF RELATIVELY SHARP CURVES IN A SECTION ON WHICH CURVES ARE INFREQUENT INCREASES THE ACCIDENT POTENTIAL. IT HAS BEEN SHOWN THAT WHEN EXISTING SHARP CURVES ARE IMPROVED THROUGH RECONSTRUCTION THE NUMBER OF ACCIDENTS AND THE DEGREE OF ACCIDENT SEVERITY CAN BE REDUCED. IT IS CONCLUDED THAT VERTICAL ALIGNMENT IS RELATED TO SAFETY, ESPECIALLY THE STEEPER GRADES. ALTHOUGH THE RELATIVE EFFECTS OF DOWNGRADES AND UPGRADES ARE NOT COMPLETELY CLEAR, THE ACCIDENT RATE APPEARS TO INCREASE WITH INCREASING ROAD GRADIENT. THE EFFECT OF INCREASED ACCIDENT RATES FOR REDUCED SIGN DISTANCES IN TRANSITIONAL CREST AND SAG SECTIONS HAS ALSO BEEN DEMONSTRATED. THE RELATIVE EFFECT OF ALIGNMENT ON SAFETY HAS BEEN REPORTED IN SEVERAL RECENT STUDIES. ALTHOUGH BOTH HORIZONTAL AND VERTICAL ALIGNMENT FACTORS HAVE BEEN FOUND TO BE STRONGLY RELATED TO SAFETY SEPARATELY, THE RELATION OF ALIGNMENT RELATIVE TO OTHER CONTROL AND DESIGN FACTORS IS NOT CLEAR. HOWEVER, SHARP HORIZONTAL CURVATURE IN COMBINATION WITH OTHER CRITICAL FEATURES SUCH AS INTERSECTIONS AND TRAFFIC VOLUME HAS BEEN FOUND TO HAVE AN IMPORTANT RELATIONSHIP TO SAFETY. TRAFFIC CONTROL DEVICES HAVE BEEN FOUND TO REDUCE ACCIDENTS ON HORIZONTAL CURVES. BOTH CURVE WARNING SIGNS WITH ADVISORY SPEED SIGNS AND ROADSIDE DELINEATORS HAVE BEEN FOUND EFFECTIVE, ESPECIALLY AT LOCATIONS WITH HIGH ACCIDENT RATES.

• Supplemental Notes:
  • The Automotive Safety Foundation Published the first three chapters in this series. The remaining chapters were published by the Highway Users Federation for Safety and Mobility.
• Corporate Authors:

  Highway Users Federation for Safety and Mobility

  1776 Massachusetts Avenue, NW
  Washington, DC  United States  20036
• Authors:
  • Leisch, J E
• Publication Date: 1971

Media Info

• Features: Figures; References; Tables;
• Pagination: 19 p.

Subject/Index Terms

• TRT Terms: Alignment; Crash rates; Curvature; Curves (Geometry); Sight distance; Slopes; Speed; Traffic control devices; Warning signs
• Uncontrolled Terms: Grades; Horizontal curvature; Vertical curvature
• Subject Areas: Highways; Safety and Human Factors;

Filing Info

• Accession Number: 00221383
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 27 1971 12:00AM