STATE OF THE ART RELATED TO SAFETY CRITERIA FOR HIGHWAY CURVE DESIGN

AN EXAMINATION OF THE STATE OF KNOWLEDGE WAS CONDUCTED FOR THE PURPOSE OF EVALUATING THE VALIDITY OF DESIGN CRITERIA FOR HORIZONTAL HIGHWAY CURVES. THE EVALUATION WAS SPECIFICALLY CONCERNED WITH THE DESIGN EQUATION (CENTRIPETAL), ASSUMED LEVELS OF TIRE-PAVEMENT SIDE FRICTION CAPABILITY, SAFE SIDE FRICTION FACTORS, MAXIMUM DEGREE OF CURVATURE, MAXIMUM SUPER ELEVATION, AND DESIGN FACTORS OF SAFETY. THE EVALUATION WAS ADDRESSED TO DESIGN CRITERIA AS PRESENTED IN "A POLICY ON GEOMETRIC DESIGN OF RURAL HIGHWAYS, 1965," BY THE AASHO. THE MAJOR FINDINGS WERE: (1) IT APPEARS THAT MINIMUM CURVE DESIGN STANDARDS (THOSE EMPLOYED BY MOST STATE HIGHWAY DEPARTMENTS) DO NOT PROVIDE AN ADEQUATE FACTOR OF SAFETY FOR THE RANGE IN OPERATIONAL CONDITIONS ENCOUNTERED ON THE HIGHWAYS, (2) THE STANDARD CENTRIPETAL FORCE EQUATION IS REASONABLY VALID IF THE CURVE RADIUS IS LARGELY RELATIVE TO THE DIMENSIONS OF THE VEHICLE. ITS VALIDITY HAS NOT BEEN SUBSTANTIATED FOR CURVES GREATER THAN 4-DEGREES, (3) THE "TYPICAL" RELATIONSHIP BETWEEN TIRE- PAVEMENT FRICTION CAPABILITY AND VEHICLE SPEED EMPLOYED BY THE AASHO POLICY HAS NO OBJECTIVE RELATION TO ACTUAL HIGHWAY CONDITIONS. MEASUREMENTS MADE IN ONE STATE INDICATE THAT ONLY 55 PERCENT OF THE STATE'S PAVEMENTS SATISFY THIS "TYPICAL" FRICTION CAPABILITY LEVEL, (4) THE USE OF LOCKED- WHEEL SKID TRAILERS TO MEASURE THE SIDE FRICTION CAPABILITY OF A PAVEMENT IS A QUESTIONABLE PRACTICE, (5) THE USE OF FRICTION DEMAND DESIGN VALUES THAT CORRESPOND TO THAT POINT AT WHICH SIDE FORCES CAUSE DRIVER DISCOMFORT HAS NO OBJECTIVE FACTOR OF SAFETY RELATIONSHIP TO THE SIDE FRICTION CAPABILITY OF THE TIRE-PAVEMENT INTERFACE, (6) THE AASHO POLICY EMPLOYS THE EXPLICIT ASSUMPTION THAT VEHICLES WILL FOLLOW THE DESIGNED PATH OF THE HIGHWAY CURVE WITH GEOMETRIC EXACTNESS. THIS ASSUMPTION DOES NOT ACCOUNT FOR CORRECTIVE MANEUVERS THAT ARE OCCASIONALLY FOUND NECESSARY WHEN DRIVERS HAVE MISJUDGED THE DEGREE OF THE HIGHWAY CURVE, (7) THERE ARE SEVERAL OTHER VARIABLES, NOT EXPLICITLY DESIGNED FOR, THAT WILL REDUCE THE ASSUMED FACTOR OF SAFETY, AND (8) THE REPORT RECOMMENDS UPGRADING MINIMUM CURVE DESIGN STANDARDS ON A PROVISIONAL BASIS AND CONCURS WITH THE VALUES RECENTLY ADOPTED BY THE TEXAS HIGHWAY DEPARTMENT. /AUTHOR/

• Supplemental Notes:
  • Res Rpt No 134-4, 99 PP, 28 FIG, 9 TAB, 31 REF, 4 APP
• Corporate Authors:

  Texas Transportation Institute

  Texas A&M University System, 1600 E Lamar Boulevard
  Arlington, TX  United States  76011
• Authors:
  • Glennon, J C
• Publication Date: 1969-11

Subject/Index Terms

• TRT Terms: Curvature; Curves (Geometry); Design; Friction; Geometric design; Safety factors; State of the art studies; Superelevation
• Uncontrolled Terms: Design criteria; Horizontal curvature
• Subject Areas: Design; Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 00225759
• Record Type: Publication
• Files: TRIS
• Created Date: Jun 22 1970 12:00AM