BRAKING DISTANCES OF VEHICLES FROM HIGH SPEEDS

BRAKING DISTANCES WERE MEASURED FOR 53 PASSENGER CARS MAKING STOPS FROM SPEEDS RANGING FROM 20 TO 90 MPH ON A CONCRETE SURFACE. THE AVERAGE DISTANCES TRAVELED AFTER THE BRAKES HAD BEEN APPLIED WERE 22 FT FROM A SPEED OF 20 MPH, 130 FT FROM 50 MPH, AND 585 FT FROM 90 MPH. SOME OF THE PASSENGER CARS REQUIRED MORE THAN 600 FT TO STOP FROM 75 MPH. DURING THE TESTS, INFORMATION WAS OBTAINED ON THE ACCELERATION RATES OF PASSENGER CARS, THE REACTION TIME OF DRIVERS, AND THE EFFECT OF BRAKE FADE OR THE TEMPORARY REDUCTION OF BRAKE EFFECTIVENESS RESULTING FROM HEAT. IN AN EFFORT TO RELATE THE BRAKING DISTANCES OF THE VEHICLES TO THE COEFFICIENT OF FRICTION BETWEEN THE TIRES AND THE ROAD SURFACE, EQUIPMENT WAS DEVELOPED TO MEASURE COEFFICIENTS OF FRICTION OF ROAD SURFACES. COMPARISONS WERE OBTAINED FOR DIFFERENT TYPES OF ROAD SURFACES WHEN DRY AND WET AND FOR DIFFERENT TIRES. IT WAS FOUND, FOR EXAMPLE, THAT SOME SURFACES WHICH HAD THE HIGHEST FRICTION COEFFICIENTS WHEN DRY HAD THE LOWEST COEFFICIENTS WHEN WET. IT WAS ALSO FOUND THAT TWO SETS OF TIRES WHICH HAD IDENTICAL TREAD PATTERNS AND CONSISTED OF THE SAME RUBBER COMPOUND COULD CAUSE A DIFFERENCE OF 30 PERCENT IN BRAKING DISTANCE. /AUTHOR/