APPLICATION OF VEHICLE OPERATING CHARACTERISTICS TO GEOMETRIC DESIGN AND TRAFFIC CONDITIONS

FIVE NATIONALLY USED REFERENCE BOOKS FOR HIGHWAY DESIGN AND TRAFFIC OPERATIONS PROCEDURES AND THREE TYPICAL STATE HIGHWAY MANUALS WERE REVIEWED TO DETERMINE WHERE PRACTICE MIGHT BE AFFECTED BY VEHICLE CHARACTERISTICS, PARTICULARLY AS THESE CHARACTERISTICS CHANGE WITH SUCCESSIVE DESIGNS OR ARE PERFORMANCE CAPABILITIES THAT ARE MODIFIED BY DRIVER PREFERENCE. SINCE VEHICLE CHARACTERISTICS CHANGE OVER A PERIOD OF YEARS, A NEED WAS EXPRESSED TO UPDATE VEHICLE PERFORMANCE DATA FOR THE PURPOSE OF UPDATING DESIGN CRITERIA AND TRAFFIC OPERATIONS PROCEDURES. HIGHWAY DESIGN CRITERIA AND TRAFFIC OPERATIONS PROCEDURES REQUIRE A KNOWLEDGE OF MOTOR VEHICLE CHARACTERISTICS. ALL DESIGN AND OPERATING CHARACTERISTICS OF VEHICLES THAT INTERACT WITH THE HIGHWAY DESIGN AND TRAFFIC OPERATIONS PROCEDURES ARE LISTED AND DISCUSSED. DETAILED DISCUSSIONS ARE PRESENTED OF ADDITIONAL CONSIDERATIONS THAT ARE FELT TO BE APPROPRIATE TO SOME GEOMETRIC STANDARDS AND OPERATING PROCEDURES. NO STANDARDS OR PROCEDURES WERE FOUND TO EXIST IN WHICH CHANGES APPEARED TO BE MANDATORY BECAUSE OF CHANGES IN VEHICLES. PRACTICALLY ALL OF THE RECOMMENDATIONS THAT HAVE BEEN MADE FOR RECONSIDERATION AND REVIEW, OR ESTABLISHMENT OF NEW STANDARDS, DERIVE FROM INCREASED TECHNICAL KNOWLEDGE CONCERNING THE RELATIONSHIP OF THE VEHICLE TO THE HIGHWAY AND TO TRAFFIC OPERATIONS. STATISTICALLY DERIVED PROBABILITIES OF APPEARANCES ARE THE FOUNDATIONS FOR OTHER RECOMMENDATIONS. AN EXAMPLE OF THE FIRST KIND IS THE TAKING INTO ACCOUNT FIELD OF VISION FROM THE VEHICLE WHEN DETERMINING CLEARANCE OF OBSTACLES AS A FACTOR IN LANE-WIDTH REQUIREMENTS. AN EXAMPLE OF THE SECOND KIND IS THE DETERMINATION OF THE RELATIVE LIKELIHOOD AND CONSEQUENCES OF SKIDDING ON A CURVE WITH SUPERELEVATION, EITHER WHEN THE VEHICLE IS STOPPED ON AN ICY SURFACE OR SKIDS ON THAT SURFACE AS A RESULT OF EXCESSIVE CENTRIFUGAL FORCE. DRIVER-MODIFIED PERFORMANCE CAPABILITIES OF VEHICLES LEAD TO STILL OTHER RECOMMENDATIONS. TYPICAL EXAMPLES ARE: TAKING INTO ACCOUNT BODY-ROLL ANGLE WHEN DETERMINING MINIMUM RADIUS OF CURVATURE OF A HORIZONTAL CURVE BY THE BALL-BANK INDICATOR METHOD, AND THE SETTING OF THE LENGTH OF THE AMBER PHASE OF THE TRAFFIC SIGNAL, AS A FUNCTION OF APPROACH SPEED. CONCLUSION IS MADE THAT MOST HIGHWAY DESIGN FEATURES AND TRAFFIC OPERATIONS PROCEDURES THAT RELATE TO VEHICLE CHARACTERISTICS ARE GOVERNED BY STANDARDS THAT ARE SATISFACTORY. THE DETAILED INVESTIGATION OF HOW VEHICLE DESIGN CHARACTERISTICS RELATE TO HIGHWAY GEOMETRICS UNDERSCORES THE NEED FOR STABILIZING THE VEHICLE CHARACTERISTICS. IT IS FELT THAT SOME VEHICLE DESIGN STANDARDS SHOULD BE IMPOSED ON THE INDUSTRY. /AUTHOR/