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The inclusion of automobiles in the Florida skid correlation study was prompted by the recognition of the following needs: 1) to compare stopping-distance measurements obtained with different instrumentation, 2) to suggest a standard method of stopping-distance testing, 3) to relate skid-resistance measurements of trailer-type testers with stopping distances of automobiles, and 4) to explore other skid-resistance measurement techniques using an automobile.
The vehicles were all full-size automobiles. Each vehicle was instrumented to measure a distance from a predetermined pressure in the brake hydraulic system to where the vehicle came to rest. Stopping distance in most of the automobiles was read directly from summating counters. Two of the automobiles were equipped with strip-chart recorders to measure distance, velocity and deceleration during the skid.
The measured stopping distances displayed minor differences between automobiles regardless of the instrumentation. The primary cause of variation in the test results was attributed to the inability of the driver to apply brakes at the prescribed test velocity. Lag between brake application and wheel lock and errors in the distance-measurement instrumentation were of secondary concern.
The stopping-distance data were correlated with the trailer-measured skid resistances for several velocities. Approximate stopping distance, therefore, can be predicted from trailer tests, or vice versa.
The results of the stopping-distance tests were sufficiently encouraging to consider standarization. Adoption of a standard method of test would serve several useful purposes. The principal benefits would be derived from having a reliable, alternate method of skid testing and references to “stopping distance” of automobiles would acquire a uniform understanding of the measurement and, therefore, common usage of the term.
testing, stopping distance, skid resistance, friction, skid, automobiles, trailers, correlation, pavements, highways
Rizenbergs, R. L.
Chief Research Engineer, Kentucky Department of Highways, Lexington, Kentucky