1、Designation: E2341/E2341M 05 (Reapproved 2014)Standard Test Method forDetermining the Stopping Distance Number by Initial Speedand Stopping Distance at Traffic Incident Sites1This standard is issued under the fixed designation E2341/E2341M; the number immediately following the designation indicates
2、the yearof original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of an aver
3、agestopping distance number (SDN) under the conditions that thismethod was executed. The experimental conditions are gener-ally intended to be similar to those of a specified trafficincident. The data from this method is not comparable tomeasured distances of a specified traffic incident vehicle tha
4、tcannot be shown to have continuous, full application of itsbraking system.1.2 This test method determines the SDN from the mea-sured stopping distance and initial speed when the wheels onspecified axles are braked in the same manner as the specifiedtraffic incident vehicle. The evaluation vehicles
5、braking sys-tem is required to duplicate the specified incident vehicle forboth type (conventional, partial ABS, or full ABS) and func-tionality (all brakes functional or not).1.3 The method documents the test conditions as a basis forevaluating their similarity to conditions of a specified traffici
6、ncident.1.4 The values stated in either inch-pound units or SI unitsare to be regarded separately as standard. Within the test, the SIunits are shown in brackets. The values stated in each systemare not exact equivalents; therefore, each system must be usedindependently of the other. Combining value
7、s from the twosystems may result in nonconformance with the specification.1.5 This standard may involve hazardous materials,operations, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this sta
8、ndard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E178 Practice for Dealing With Outlying ObservationsE274 Test Method for Skid Resistance of Paved SurfacesUsing a Full-Scale Ti
9、reF403 Test Method for Tires for Wet Traction in Straight-Ahead Braking, Using Highway Vehicles (Withdrawn2007)3F457 Test Method for Speed and Distance Calibration ofFifth Wheel Equipped With Either Analog or DigitalInstrumentation3. Summary of Test Method3.1 The test apparatus consists of a vehicle
10、 and tires similarto the traffic incident vehicle and instruments to measure andrecord initial speed and stopping distance. If the incidentvehicle did not have ABS and the test vehicle does, the ABSmust be disabled.3.2 The test is performed on the roadway where the trafficincident occurred with surf
11、ace conditions similar to those thatexisted at the time of the traffic incident.3.3 The test vehicle is brought above the desired test speedand permitted to coast onto the test section. The brakes are thenvery quickly and forcefully applied to cause immediate lock-upof all desired wheels and to skid
12、 to a stop (note: if the car isequipped with ABS, lock-up will not be obtained). In eithercase the initial speed at brake application, the stoppingdistance, and tire mark lengths are recorded. If tire marks donot vary smoothly in darkness, width or density, the variationin appearance needs to be des
13、cribed.3.4 The deceleration of the roadway/vehicle combination,called the stopping distance number (SDN), is determined from1This test method is under the jurisdiction of ASTM Committee E17 on Vehicle- Pavement Systems and is the direct responsibility of Subcommittee E17.21 onField Methods for Measu
14、ring Tire Pavement Friction.Current edition approved Dec. 1, 2014. Published December 2014. Originallyapproved in 2005. Last previous edition approved in 2009 as E2341/E2341M 05(2009). DOI: 10.1520/E2341_E2341M-05R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AST
15、M Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、C700, West Conshohocken, PA 19428-2959. United States1the measured stopping distance and the initial speed. SDNdiffers from skid resistance since it includes other factors suchas grade, air resistance, and rolling resistance, especially fornon-locked wheels.NOTE 1Since speed has a significant effect
17、 on pavement surface skidresistance measurements, the SDN can be expected to be considerablydifferent at higher speeds from that at lower speeds as well. Generally, theSDN can be expected to decrease with increasing speed.4. Significance and Use4.1 The SDN determined by this method represents anaver
18、age over the interval from the beginning of brake applica-tion to the rest position. It may be a reasonable estimate of theSDN during one or more portions of the specified trafficincident if the test conditions and the incident conditions aresufficiently similar. Since this standard determines an av
19、erageSDN from the initial speed to rest, care should be exercised inany application of the test results to a portion of the incidentthat does not end with the specified traffic incident vehicle atrest.4.2 The uncertainty of the SDN determined by this methodcan be evaluated by procedures shown in thi
20、s method. Therelationship between the SDN of this test method and the SDNof a specified traffic incident is beyond the scope of thismethod. The similarity between test and specified trafficincident SDNs depends on the similarity of vehicles, vehicleballast conditions, vehicle weight transfer during
21、braking,vehicle tires, pavement surface, pavement surfacecontamination, and vehicle speed during a particular phase ofthe incident sequence.4.3 The SDN determined by this method does not necessar-ily agree or correlate directly with other methods of skidresistance measurements, such as Test Method E
22、274. This testmethod is suitable for those situations where adequate similar-ity can be shown.4.4 When it is known that a particular wheel brake was notfunctional during the incident, the method provides for only thedesired wheels to be braked on the test vehicle to duplicate thespecified traffic in
23、cident vehicle.5. Test Equipment5.1 Test VehicleThe evaluation vehicle that is intended toduplicate the performance characteristics of the specified trafficincident vehicle. The test vehicle should be similar to theincident vehicle because the test vehicles performance char-acteristics cannot be rem
24、oved from the SDN and will bedifferent than the specified traffic incident vehicle. The trafficincident vehicle should be used, however, this is often notpractical. Therefore, the test vehicle must be as close to thesame year, make, and model, and be equipped with the sameoptions as possible.5.1.1 W
25、eight and Weight DistributionThe load the vehicleplaces on each of its supporting tires while the vehicle is at rest.The total vehicle weight should be similar to that of theincident vehicle. The static weight distribution should besimilar to the incident vehicle. The height of the center of mass,th
26、e wheelbase, and the inertial mass should be similar to thoseof the traffic incident vehicle.5.1.2 Braking SystemThe test vehicle brakes should besimilar to those of the incident vehicle, that is, drum, disk,ABS, and so forth. If the brake system is not ABS, the driverand brake system must be capabl
27、e of locking all desired wheelsduring a stop.5.1.3 TiresTest tires must be similar to those in thespecified traffic incident. Tires, depending on their specificperformance balance, can vary substantially in their brakingperformance. Every effort should be made to duplicate the tireon the specified t
28、raffic incident vehicle. The test vehicle tiresshould match by manufacturer, brand name, tire line, tire sizeand UTQG (Uniform Tire Quality Grade) ratings, construction(bias, radial, and so forth), state of wear and inflation pressuresshould be as similar as is reasonable. Whenever possible, thetire
29、s from the specified traffic incident vehicle should be usedon the test vehicle. (Also see Test Method F403.)5.2 Instrumentation:5.2.1 Vehicle Initial Speed Measuring DeviceThe testvehicle shall be equipped with devices capable of measuringand holding the value of the speed immediately prior to theb
30、raking interval. The speed-indicating device shall provide aspeed resolution and accuracy of 61 mph 61.5 km/h. Anappropriately calibrated vehicle speedometer, an on-boardradar gun, or fifth wheel are suitable speed measuring devices.The initial speed memory device must be a suitably calibratedcontin
31、uous recording device attached to the speed indicatingdevice or an operator who observes the speed display continu-ously and notes the value at the initiation of braking. Thevehicle speedometer does not usually have the required accu-racy.5.2.2 Distance Measuring DeviceThe distance from theinitiatio
32、n of braking to the rest position shall be measured by adevice with a fractional uncertainty equal to or less than thefractional uncertainty of the speed measuring device (forexample, for 40 6 1 mph 65 6 2 km/h the fractionaluncertainty is 61/40 = 62.5 % or 1.25 ft in 50 ft 0.5 m in 20m). A steel ta
33、pe or a fifth wheel are suitable devices. If a fifthwheel assembly with speed and distance readouts is used, itshould meet the requirements specified in Test Method F457.Ifa tape is used, then a device similar to the American Automo-bile Association (AAA) marker must be used to mark thepavement when
34、 brake pedal pressure is applied and measure-ment is made from the mark to the final resting point of thevehicle.5.2.3 Initial Braking Event MarkerA device capable ofmarking the pavement or initiating a distance counter at thebeginning of the braking intervals would be installed on thevehicle. The d
35、evice may be actuated by the initial motion of thebrake pedal, contact force on the brake pedal, or brake systempressure of 25 psi 170 kPa for fully hydraulic brake systems.NOTE 2The time difference between initial pedal motion and thebeginning of braking is nominally less than 0.1 s which correspon
36、ds toless than 6 ft at 40 mph 1.83 m at 65 km/h.On airbrake systems, only a pressure switch in the serviceline shall be used. A gun powder cartridge device similar to anAAA marker is a suitable device for marking the pavement.The actual event used to indicate the beginning of the brakinginterval sha
37、ll be reported.E2341/E2341M 05 (2014)25.2.4 Pressure-Sensitive SwitchA pressure-sensitiveswitch, such as a hydraulic brake-light switch, requiring 70 to90 psi 480 to 620 kPa pressure to close, should be installed inthe hydraulic brake system or the brake pedal to actuate thestopping-distance counter
38、 or mark the pavement if the distancemeasuring system is not automatic.6. Calibration6.1 SpeedCalibrate the test vehicle speed indicator atspeeds which bound the range intended for the test. Locate twomarkers on a reasonably straight level roadway that are ameasured distance apart (within 61 % uncer
39、tainty). The mini-mum distance is the distance traveled in 45 s at the calibrationspeed (about 0.5 mile for 40 mph 0.8 km for 65 km/h). Fortwo speeds which bound the calibration range and at least twoother speeds in the range, operate the vehicle at constant speedthrough the marked section measuring
40、 the travel time betweenmarkers (60.5 s) and speed (60.5 mph 60.8 km/h). If theinstantaneous speed varies from the average by more than 1mph, discard that run. The calibrated speed is determined froma least-squares line fit to the measured and indicated data.Radar guns and other electronic speed mea
41、suring devicesshould be calibrated by the manufacturers recommendedmethod.6.2 DistanceCalibrate the fifth-wheel distance transducersand counters over a measured distance at least 200 6 1 ft 60.06 0.3 m. The counter should correctly indicate the measureddistance 60.5 % or the counter results for the
42、SDN test shouldbe corrected for the calibration error, that is, test count timecalibration count/calibration distance. Fifth wheels should becalibrated per Test Method F457.NOTE 3A steel tape in good condition does not need to be calibrated.7. Test Site7.1 Surface ConditionThe roadway surface should
43、 be thesame surface present during the specified traffic incident exceptfor normal wear. If the surface during the specified trafficincident was not clean and dry, the material contaminating thesurface must be characterized and pavement contaminationsimilar to that during the specified traffic incid
44、ent applied to thetest surface.NOTE 4A roadway surface that is wetted and tested after an extendeddry period may not exhibit the same SDN after the surface has beenthoroughly rain washed.7.2 Pavement WettingIf the incident surface was wet, thetest surface should be wetted to obtain similar water dep
45、th ordrained conditions. When water is applied artificially, wet thetest lane at the test site just prior to SDN testing using a waterwagon equipped with spray bar or other means of distributingwater evenly and rapidly. Make two or more applications ofwater with a minimum coverage of 0.015 gal/ft20.
46、6 L/m2 615 % per application until the surface is well saturated (surfacecavities are filled with water and runoff results). Wet asufficiently long segment of the test lane to permit the testvehicle to skid on a wet surface and to allow the driver to adjustthe speed before brake application. Repeate
47、d application ofwater to the test lane between each test as required to maintainsimilar wetness conditions. If other contaminates were presentduring the accident, they should be duplicated as closely aspossible. If the accident occurred on dry pavement, no wettingis required.7.3 Positioning of Test
48、Vehicle on HighwayNormally, thetest should be performed in the same lane/lanes traveled by thespecified traffic incident vehicle with the path of travel beingthe same. Where this is not possible, separate measurementsmust be made on each section of different frictional propertiesin the same directio
49、n of travel as the incident vehicle.7.4 Test SpeedThe standard test speed should be that ofthe specified traffic incident vehicle. If the speed is not known,a test should be conducted at 30 mph 50 km/h. From this test,an estimated speed can be calculated and the test should bererun at the calculated speed. If the specified traffic incidentvehicle speed is greater than the speed limit, the speed limitshould be used. It should be noted that the SDN measured atthe lower speed might be higher and, therefore, gives a higherestimated speed or a l
