Standard Test Method for Determining the Stopping Distance Number by Initial Speed and Stopping Distance at Traffic Incident Sites

Abstract

4.1 The SDN determined by this method represents an average over the interval from the beginning of brake application to the rest position. It may be a reasonable estimate of the SDN during one or more portions of the specified traffic incident if the test conditions and the incident conditions are sufficiently similar. Since this standard determines an average SDN from the initial speed to rest, care should be exercised in any application of the test results to a portion of the incident that does not end with the specified traffic incident vehicle at rest. 4.2 The uncertainty of the SDN determined by this method can be evaluated by procedures shown in this method. The relationship between the SDN of this test method and the SDN of a specified traffic incident is beyond the scope of this method. The similarity between test and specified traffic incident SDNs depends on the similarity of vehicles, vehicle ballast conditions, vehicle weight transfer during braking, vehicle tires, pavement surface, pavement surface contamination, and vehicle speed during a particular phase of the incident sequence. 4.3 The SDN determined by this method does not necessarily agree or correlate directly with other methods of skid resistance measurements, such as Test Method E274/E274M. This test method is suitable for those situations where adequate similarity can be shown. 4.4 When it is known that a particular wheel brake was not functional during the incident, the method provides for only the desired wheels to be braked on the test vehicle to duplicate the specified traffic incident vehicle.