Some effects of measurement errors in estimating involvement rate as a function of deviation from mean traffic speed

Abstract

INVOLVEMENT RATE IS COMMONLY USED AS A MEASURE OF ACCIDENT RISK. WHENEVER INVOLVEMENT RATE IS EXPRESSED AS A FUNCTION OF THE DEVIATION OF THE SPEED OF THE ACCIDENT-INVOLVED VEHICLE FROM THE MEAN TRAFFIC SPEED, ERRORS OF MEASUREMENT BECOME EXTREMELY IMPORTANT. THE EFFECTS OF MEASUREMENT ERRORS HAVE BEEN EXAMINED AND THE RESULTS INDICATE THAT ERRORS IN ESTIMATING SPEEDS OF ACCIDENT-INVOLVED VEHICLE CAUSES THE INVOLVEMENT RATE, WHEN PLOTTED AS A FUNCTION OF SPEED DEVIATION, TO BE U-SHAPED AND THUS OVERESTIMATED FOR LARGE DEVIATIONS AND UNDERESTIMATED FOR SMALL DEVIATIONS. A BIAS IN ESTIMATING SPEEDS ALSO HAS A SIGNIFICANT EFFECT ON THE INVOLVEMENT RATE VERSUS SPEED DEVIATION RELATIONSHIP. EXAMPLES ARE GIVEN TO ILLUSTRATE THE EFFECTS OF MEASUREMENT ERRORS. /HSL/