ASTM E2341 E2341M-2005 Standard Test Method for Determining the Stopping Distance Number by Initial Speed and Stopping Distance at Traffic Incident Sites.pdf

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1、Designation: E 2341/E 2341M 05Standard Test Method forDetermining the Stopping Distance Number by Initial Speedand Stopping Distance at Traffic Incident Sites1This standard is issued under the fixed designation E 2341/E 2341M; the number immediately following the designation indicates theyear of ori

2、ginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of an averagestopping d

3、istance 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 thatcannot be sh

4、own 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 braking sys-t

5、em 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 trafficincident.1.4 T

6、he 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 values from the tw

7、osystems may result in nonconformance with the specification.1.5 This standard may involve hazardous materials, opera-tions, 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 standard toest

8、ablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 178 Practice for Dealing with Outlying ObservationsE 274 Test Method for Skid Resistance of Paved SurfacesUsing a Full-scale TireF 403 T

9、est Method for Tires for Wet Traction in Straight-Ahead Braking, Using Highway VehiclesF 457 Test Method for Speed and Distance Calibration of aFifth Wheel Equipped with Either Analog or DigitalInstrumentation3. Summary of Test Method3.1 The test apparatus consists of a vehicle and tires similarto t

10、he 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 surface conditions similar

11、 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 to a stop (note: if t

12、he car isequipped with ABS, lock-up will not be obtained). In eithercase the initial speed at brake application, the stopping dis-tance, and tire mark lengths are recorded. If tire marks do notvary smoothly in darkness, width or density, the variation inappearance needs to be described.3.4 The decel

13、eration of the roadway/vehicle combination,called the stopping distance number (SDN), is determined fromthe 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

14、 wheels.NOTE 1Since speed has a significant effect 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 T

15、he SDN determined by this method represents anaverage 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 are1This te

16、st method is under the jurisdiction of ASTM Committee E17 onVehicle-Pavement Systems and is the direct responsibility of Subcommittee E17.21on Field Methods for Measuring Tire Pavement Friction.Current edition approved Feb. 1, 2005. Published February 2005.2For referenced ASTM standards, visit the A

17、STM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Uni

18、ted States.sufficiently similar. Since this standard determines an averageSDN 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

19、 determined by this methodcan be evaluated by procedures shown in this 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

20、 vehicles, vehicleballast conditions, vehicle weight transfer during braking,vehicle tires, pavement surface, pavement surface contamina-tion, and vehicle speed during a particular phase of the incidentsequence.4.3 The SDN determined by this method does not necessar-ily agree or correlate directly w

21、ith other methods of skidresistance measurements, such as Test Method E 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 whee

22、ls to be braked on the test vehicle to duplicate thespecified traffic incident 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 vehi

23、cle because the test vehicles performance char-acteristics cannot be removed 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, m

24、ake, and model, and be equipped with the sameoptions as possible.5.1.1 Weight 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 shoul

25、d besimilar to the incident vehicle. The height of the center of mass,the 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. I

26、f the brake system is not ABS, the driverand brake system must be capable 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 brakingperforma

27、nce. Every effort should be made to duplicate the tireon the specified traffic 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 pr

28、essuresshould be as similar as is reasonable. Whenever possible, thetires from the specified traffic incident vehicle should be usedon the test vehicle. (Also see Test Method F 403.)5.2 Instrumentation:5.2.1 Vehicle Initial Speed Measuring DeviceThe testvehicle shall be equipped with devices capable

29、 of measuringand holding the value of the speed immediately prior to thebraking 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 de

30、vices.The initial speed memory device must be a suitably calibratedcontinuous 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 require

31、d accu-racy.5.2.2 Distance Measuring DeviceThe distance from theinitiation 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 fractionalun

32、certainty is 61/40 = 62.5 % or 1.25 ft in 50 ft 0.5 m in 20m). A steel tape 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 F 457.If a tape is used, then a device similar to the American

33、Automobile Association (AAA) marker must be used to markthe pavement when brake pedal pressure is applied andmeasurement is made from the mark to the final resting pointof the vehicle.5.2.3 Initial Braking Event MarkerA device capable ofmarking the pavement or initiating a distance counter at thebeg

34、inning of the braking intervals would be installed on thevehicle. The device 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 a

35、nd thebeginning of braking is nominally less than 0.1 s which corresponds 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

36、 actual event used to indicate the beginning of the brakinginterval shall be reported.5.2.4 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 bra

37、ke pedal to actuate thestopping-distance counter 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

38、 are ameasured distance apart (within 61 % uncertainty). 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 co

39、nstant speedE 2341/E 2341M 052through the marked section measuring 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 mea

40、sured and indicated data.Radar guns and other electronic speed measuring devicesshould be calibrated by the manufacturers recommendedmethod.6.2 DistanceCalibrate the fifth-wheel distance transduc-ers and counters over a measured distance at least 200 6 1ft60.0 6 0.3 m. The counter should correctly i

41、ndicate themeasured distance 60.5 % or the counter results for the SDNtest should be corrected for the calibration error, that is, testcount time calibration count/calibration distance. Fifth wheelsshould be calibrated per Test Method E 457.NOTE 3A steel tape in good condition does not need to be ca

42、librated.7. Test Site7.1 Surface ConditionThe roadway surface should 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 pave

43、ment contaminationsimilar to that during the specified traffic incident 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 w

44、as wet, thetest surface should be wetted to obtain similar water depth 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

45、more applications ofwater with a minimum coverage of 0.015 gal/ft20.6 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 a

46、llow the driver to adjustthe speed before brake application. Repeated 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 occu

47、rred on dry pavement, no wettingis required.7.3 Positioning of Test 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

48、 each section of different frictional propertiesin the same direction 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 s

49、peed 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 longer stopping distance, SD, estimate. Atspeeds above 40 mph 65 km/h, caution should be used wherethe site is not clear and straight.8. Procedure8.1 When the vehicle, instruments, and test surfaces areready, drive the vehicle toward