Tire-roadway frictional drag, an important consideration for transportation accident reconstruction, is dependant on vehicle, roadway and environmental factors. Vehicle factors include vehicle specific properties such as geometry and inertial parameters, braking system type, tire size, and tire properties. Roadway factors include grade, pavement type, construction, pavement age and other parameters. Environmental factors include temperature and inclement weather. In order to control these (and other) vehicle, roadway and environmental factors, the determination of tire-roadway frictional drag is done through staged testing using an instrumented vehicle. Staged testing is typically performed with an exemplar vehicle on a similar roadway under comparable environmental conditions. Engineering instrumentation includes acceleration and velocity sensors as well as a brake gun to directly measure total braking distance. The paper describes the utilization and application of full scale testing to determine tire-road friction under locked wheel braking on asphalt roadways. Instrumentation factors, including sampling rate, sensor accuracy, and sensor type are discussed. Analysis methodologies, including direct and indirect determination of test parameters, are explored. The testing was done on roadways of known paving date. Therefore, the effects of pavement factors such as age and construction on the determination of tire-roadway fricitonal drag are studied. Locked wheel braking tests employ direct measurements for acceleration, velocity and braking distance. Newly laid asphalt in this test series exhibits lower frictional drag values than well traveled and aged asphalt. The results form this test series demonstrate lower frictional drag factors than previously published for new asphalt. Total braking distance on all tested surfaces exceeded visible skid distance. All tests exhibited a peak acceleration with a decrease to a plateau sliding value. In all tests, onset of visible skids approximately corresponded to the time at which the peak acceleration occurred. In order to calculate an accurate pre-braking speed, accident reconstruction calculations should account for the total braking distance.
The analysis and determination of tire-roadway frictional drag
2003
10 Seiten, 4 Bilder, 13 Tabellen, 20 Quellen
Conference paper
English
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