Vehicle speeds on high standard curves.

VEHICLE OPERATING SPEEDS HAVE BEEN MEASURED ON 31 HIGHWAY CURVES WITH DESIGN SPEEDS IN THE RANGE V80 TO V120 KM/H. REGRESSION ANALYSIS SHOWED THAT, FOR CARS, 71 PER CENT OF THE VARIABILITY IN 85TH PERCENTILE CURVE SPEED COULD BE EXPLAINED IN TERMS OF CURVATURE, SIGHT DISTANCE, OPPOSING FLOW AND ESTIMATES OF DESIRED TRAVEL SPEED. THE RESULTS OF THE STUDY ARE DISCUSSED IN TERMS OF THE ASSUMPTIONS UNDERLYING CURRENT GEOMETRIC DESIGN PRACTICE. THE REGRESSION EQUATION IS USED TO DEMONSTRATE THE DIFFICULTY OF PROVIDING SUPERELEVATION AND SIGHT DISTANCE ADEQUATE FOR THE LIKELY OPERATING SPEEDS ON ISOLATED CURVES OF 400M RADIUS OR LESS. (A). FOR THE COVERING ABSTRACT OF THE CONFERENCE PROCEEDINGS SEE IRRD ABSTRACT NO 226354.