Skid Testing With an Automobile

Abstract

A STANDARD SKID TEST, UTILIZING AN AUTOMOBILE INSTRUMENTED TO RECORD THE CHARACTERISTICS OF VARIOUS PARAMETERS ASSOCIATED WITH A VEHICLE IN SKID WAS DEVELOPED. THE MAJOR PARAMETERS STUDIED WERE TIME, DISTANCE, VELOCITY AND DECELERATION. IN ADDITION, INFORMATION WAS OBTAINED ON TIME OF WHEEL-LOCK, BRAKE-PEDAL APPLICATION AND THE INSTANT THE BRAKE-LIGHT WAS ENERGIZED. SKID RESISTANCE VALUES WERE DETERMINED FOR TWENTY-FIVE DIFFERENT COMBINATIONS OF THE PARAMETERS AND THEIR LEVELS. THESE VALUES WERE GROUPED INTO THREE CATEGORIES' VELOCITY AND DISTANCE, VELOCITY AND TIME, AND DECELERATION. FIVE TEST SITES HAVING DIFFERENT COMPOSITIONS AND SKID RESISTANCES WERE SELECTED FOR STUDY. EACH SITE WAS TESTED AT 40 MPH IN THREE ROUNDS DURING A TWO-MONTH PERIOD. FIVE TESTS PER SITE WERE CONDUCTED IN ROUND I AND TEN IN EACH OF THE REMAINING TWO ROUNDS. THE TEST VEHICLE WAS A 1962 FORD SEDAN EQUIPPED WITH ASTM, E-M, STANDARD TIRES INFLATED TO 24 PSI. A REGRESSION ANALYSIS WAS MADE OF THE DATA FOR EACH SET OF CONDITIONS. MAJOR CONCLUSIONS DRAWN FROM THE STUDY ARE AS FOLLOWS' 1. MEASURING TIME AND VELOCITY OF A SKIDDING AUTOMOBILE FULFILLS THE REQUIREMENTS OF AN INTERIM STANDARD METHOD OF TESTING. 2. THE USE OF AN AUTOMOBILE AS A REGULAR PAVEMENT- SLIPPERINESS TESTING DEVICE IS EXTREMELY UNSATISFACTORY IN TERMS OF TIME, EXPENSE AND HAZARD. 3. AIR RESISTANCE AND VEHICLE DYNAMICS HAVE NEGLIGIBLE EFFECTS ON SKID RESISTANCE. 4. MUCH REMAINS TO BE LEARNED CONCERNING THE VARIATION OF SKID RESISTANCE WITH SEASON, TEMPERATURE AND PAVEMENT WASHING. THE COEFFICIENT OF FRICTION OBTAINED FROM THE MEASUREMENT OF ELAPSED TIME IN THE VELOCITY INCREMENT BETWEEN 30 AND 20 MPH OF THE 40 TO 0 RANGE IN VELOCITY WAS SELECTED AS THE STANDARD BECAUSE /1/ TIME CAN BE MEASURED ACCURATELY, /2/ TEST RESULTS SHOWED GOOD REPEATABILITY /3/ CHART COULD BE READILY INTERPRETED AND /4/ COEFFICIENT OF FRICTION IN THIS VELOCITY INCREMENT IS NEARLY LINEAR. /BPR/