SKID TESTING

THE HIGHLIGHTS ARE REVIEWED OF EQUIPMENT AND TECHNIQUES FOR SKID TESTING IN THE EVALUATION OF PAVEMENT SLIPPERINESS. THE TEST METHODS REVIEWED IN DETAIL ARE THOSE WHICH PROVIDE A MEASURE OF PAVEMENT COEFFICIENT OF FRICTION AT SPEEDS IN THE ORDER OF THOSE AT WHICH MOTOR VEHICLES NORMALLY TRAVEL OVER THE PAVEMENTS. THESE TECHNIQUES FALL INTO THE FOLLOWING THREE CATEGORIES: (1) MEASUREMENT OF THE DISTANCE A VEHICLE WILL SLIDE WITH ALL WHEELS LOCKED IN COMING TO A STOP FROM A SELECTED INITIAL SPEED, (2) MEASUREMENT OF THE RATE OF DECELERATION OF A VEHICLE WHEN THE BRAKES ARE LOCKED AT A PRESELECTED SPEED, AND (3) THE USE OF A TOWED VEHICLE, USUALLY A TWO-WHEELED TRAILER, WHICH IS TOWED ACROSS THE SELECTED TEST SITE AT SOME PREDETERMINED SPEED. ONE OR MORE WHEELS ON THE TEST TRAILER ARE LOCKED AND ONE OF A VARIETY OF POSSIBLE MEASUREMENTS IS MADE FROM WHICH THE COEFFICIENT OF FRICTION BETWEEN THE TIRE AND SURFACE MAY BE DETERMINED. THE ADVANTAGE OF THE LOCKED-WHEEL STOPPING DISTANCE METHOD IS THE RELATIVELY LOW INITIAL COST OF EQUIPMENT AND THE EASE WITH WHICH THE EQUIPMENT CAN BE ASSEMBLED FOR USE. A FIFTH WHEEL IS ATTACHED TO THE REAR BUMPER OF THE TEST VEHICLE. THIS WHEEL GIVES A VERY ACCURATE READOUT OF VEHICLE SPEED TO ASSIST THE DRIVER IN CONTROLLING HIS SPEED. THE DISADVANTAGE OF THIS METHOD OF TEST IS THAT IT IS SOMEWHAT DANGEROUS. WHEN A VEHICLE SLIDES WITH ALL WHEELS LOCKED THE DRIVER NO LONGER HAS ANY STEERING CAPABILITY. ALTHOUGH THE INITIAL COST OF EQUIPMENT FOR THIS TYPE OF TEST IS SMALL, THE AVERAGE COST PER TEST IS QUITE HIGH BECAUSE OF THE LARGE NUMBER OF INDIVIDUALS REQUIRED TO MAKE THE TEST. THE DECELERATION METHOD RETAINS BOTH THE ADVANTAGES AND DISADVANTAGES OF THE STOPPING DISTANCE METHOD. EQUIPMENT MAY VARY FROM A TAPLEY DECELEROMETER, WHICH HAS BEEN POPULAR IN SOME STATES TO HIGHLY SOPHISTICATED DECELEROMETERS. THE SKID TRAILER METHOD REQUIRES A RELATIVELY LARGE INITIAL INVESTMENT IN EQUIPMENT. THE PRINCIPAL ADVANTAGE OF THE SKID TRAILER METHOD IS THAT OF SAFETY. VARIOUS SKID TRAILERS IN USE ARE DESCRIBED. IT IS RECOMMENDED THAT THE TRAILER SHOULD BE DESIGNED TO BE MECHANICALLY AS SIMPLE AS POSSIBLE. THE STRAIN MEASURING UNIT SHOULD BE SIMPLE, PREFERABLY PRECALIBRATED, AND SO LOCATED THAT IT MAY EASILY BE CHANGED ON THE ROAD SHOULD FAILURE IN THE UNIT OCCUR. THE TRAILER SHOULD BE EQUIPPED WITH WHEELS TO CARRY ASTM STANDARD SKID TEST TIRES. IT IS RECOMMENDED THAT ONLY ONE WHEEL BE LOCKED DURING TESTING. THIS PROVIDES A VERY STABLE OPERATION, PERMITTING SKIDS EVEN ON CURVES, AND REDUCES TIRE WEAR. A BRAKING SYSTEM MUST BE ADEQUATE TO PROVIDE RAPID LOCK-UP OF THE TEST WHEEL IN THE REPEATED SKIDS. THE ELECTRONIC SYSTEM FOR DETECTING, AMPLIFYING, AND RECORDING STRAIN MEASUREMENTS SHOULD BE SIMPLE. A TWO-MAN CREW IS RECOMMENDED FOR THESE TESTS. RESULTS HAVE SHOWN THAT SKID CORRELATION STUDIES WITH THESE TRAILERS, WITH EXPERIENCED CREWS AND WELL TESTED EQUIPMENT, CAN CORRELATE THEIR RESULTS QUITE WELL.

  • Supplemental Notes:
    • Vol 9, No 4, PP 20-24, 4 FIG, 2 REF
  • Authors:
    • Whitehurst, E A
  • Publication Date: 1969-4

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  • Accession Number: 00207029
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 2 1994 12:00AM