Standard Test Method for Determining the Stopping Distance Number by Initial Speed and Stopping Distance at Traffic Incident Sites
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.
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 SDN’s 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.
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. This test method is suitable for those situations where adequate similarity can be shown.
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.
1.1 This test method covers determination of an average stopping distance number (SDN) under the conditions that this method was executed. The experimental conditions are generally intended to be similar to those of a specified traffic incident. The data from this method is not comparable to measured distances of a specified traffic incident vehicle that cannot be shown to have continuous, full application of its braking system.
1.2 This test method determines the SDN from the measured stopping distance and initial speed when the wheels on specified axles are braked in the same manner as the specified traffic incident vehicle. The evaluation vehicle’s braking system is required to duplicate the specified incident vehicle for both type (conventional, partial ABS, or full ABS) and functionality (all brakes functional or not).
1.3 The method documents the test conditions as a basis for evaluating their similarity to conditions of a specified traffic incident.
1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the test, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.
1.5 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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