decelaration during collision

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Calculating decelaration during a car collision
  400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A.Tel: (724) 776-4841 Fax: (724) 776-5760 SAE TECHNICALPAPER SERIES  1999-01-0098Characteristic Vehicular Deceleration for KnownHazards Eric Roenitz, Andrew Happer, Ravinder Johal and Robert Overgaard INTECH Engineering Ltd. Reprinted From: Accident Reconstruction: Technology and Animation IX(SP-1407)International Congress and ExpositionDetroit, MichiganMarch 1-4, 1999  The appearance of this ISSN code at the bottom of this page indicates SAE’s consent that copies of thepaper may be made for personal or internal use of specific clients. This consent is given on the condition,however, that the copier pay a $7.00 per article copy fee through the Copyright Clearance Center, Inc.Operations Center, 222 Rosewood Drive, Danvers, MA 01923 for copying beyond that permitted by Sec-tions 107 or 108 of the U.S. Copyright Law. This consent does not extend to other kinds of copying such ascopying for general distribution, for advertising or promotional purposes, for creating new collective works,or for resale.SAE routinely stocks printed papers for a period of three years following date of publication. Direct yourorders to SAE Customer Sales and Satisfaction Department.Quantity reprint rates can be obtained from the Customer Sales and Satisfaction Department.To request permission to reprint a technical paper or permission to use copyrighted SAE publications inother works, contact the SAE Publications Group. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior writtenpermission of the publisher. ISSN 0148-7191Copyright 1999 Society of Automotive Engineers, Inc. Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solelyresponsible for the content of the paper. A process is available by which discussions will be printed with the paper if it is published inSAE Transactions. For permission to publish this paper in full or in part, contact the SAE Publications Group.Persons wishing to submit papers to be considered for presentation or publication through SAE should send the manuscript or a 300word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE. Printed in USA All SAE papers, standards, and selected books are abstracted and indexed in the Global Mobility Database   1 1999-01-0098 Characteristic Vehicular Deceleration for KnownHazards Eric Roenitz, Andrew Happer, Ravinder Johal and Robert Overgaard INTECH Engineering Ltd. Copyright © 1999 Society of Automotive Engineers, Inc. ABSTRACT This paper quantifies the deceleration of motor vehiclesas they were routinely stopped for an expected hazard ina real world environment. It was observed that the decel-eration rate varied non-linearly, with a peak value ofabout 0.25g as the vehicle decelerated through thespeed range of 20 to 30 km/h. This deceleration patternwas common to all evaluated categories of passengervehicles.A mathematical model was developed to define thedeceleration profile; enhancement of this model yieldedpredictive relations for the velocity, position and remain-ing braking time of decelerating passenger vehicles. INTRODUCTION Within the field of accident reconstruction, it is oftenadvantageous to have the driving characteristics of typi-cal vehicle operators quantified; this knowledge may formthe foundation of a specific reconstruction case or assistin the technical interpretation of witness evidence. Fortraffic/roadway engineers, the knowledge of driver behav-ior is beneficial in the design of roadways and positioningof road signs.Previous studies have addressed driver characteristicssuch as reaction time for unexpected roadway hazards[1, 2, 3, 4] and the effect of environmental factors on suchreactions [5]. Other sources have proposed estimates of “ normal ” and “ rapid ” rates of motor vehicle acceleration[6, 7] (Note: the results presented in reference 7 areincorrect as a consequence of a fundamental procedurefault). While these studies have endeavored to quantifyother driver parameters, the “ typical ” deceleration profileof vehicles during daily driving has not been adequatelydocumented.Prior to this study, only primitive information had beenavailable which considers how typical operators deceler-ate their motor vehicles for routine and expected obsta-cles. Current literature often presents a constant rate ofdeceleration for “ normal ” braking with the maximum brak-ing rate limited by the tire/roadway coefficient of friction.Precise definition of a universal motor vehicle decelera-tion pattern is impossible as many factors influence eachmotorist ’ s driving style; human factors, environmentalfactors and vehicular limitations all unquantifiably influ-ence an individual vehicle ’ s deceleration pattern. How-ever, a more precise understanding of “ typical ” vehiculardeceleration may be realized when sufficient real worlddata are considered.The purpose of this paper is to quantify the decelerationtrends of motor vehicles as they routinely stop for anexpected obstacle (i.e. a stop sign). The source data forthis study were unobtrusively collected in a real worldenvironment and are considered reflective of unalertedvehicle operator characteristics. The deceleration pat-terns of differing motor vehicle classes were compared. Ageneralized deceleration model was developed and isproposed to be representative for passenger vehicles.The data collected in this study also provide a compara-tive reference for the magnitude of acceleration/decelera-tion rates sustained by vehicles involved in sideswipecollisions and other frictional collisions that have few tan-gible analogies. REVIEW OF LITERATURE A literature search was conducted to ascertain what dataare currently available that provide insight into the char-acteristics of routine motor vehicle deceleration. Thesearch yielded numerous resources that quantify themaximum rate of vehicle deceleration as limited by tirefriction for a variety of road surfaces and environmentalconditions [8, 9, 10, 11, 12]. In addition, a series of publi-cations address the braking characteristics of motor vehi-cles under “ Emergency Braking ” conditions [13, 14, 15].However, these references do not present the rate ofdeceleration typically applied during routine braking.Fricke [6] tabulates common acceleration and decelera-tion rates. This reference introduces a value of 0.20g for “    normal braking, no skidding, ”    but does not develop thisproposal further.  2 EXPERIMENTAL PROCEDURE Decelerating vehicles were discretely monitored and theirdeceleration histories were recorded. The data collectedfrom this research were then analyzed to establish trendsand quantify the deceleration process.EXPERIMENTAL APPARATUS  –  Speed data wereacquired using a “ Stalker ” radar gun. The radar unittransmits a signal that disperses over the horizontalplane. The unit then evaluates the absolute speed of atarget from the returned signal to a precision of 0.1 km/hby applying the Doppler principle. To improve the authen-ticity of the returning signal, the radar signal dispersionand return were collimated using an aluminum aperture.This reduced the potential for the returning signal torecord extraneous reflections from background events;sources of extraneous data include secondary vehicles,pedestrians and weather related phenomena such asrain and wind blown leaves.Proper operation of the radar gun was confirmed at thestart of each test period by performing an internal hard-ware calibration; this process utilizes the unit ’ s own inter-nal electronics to verify functionality. A secondarycalibration was performed using a calibrated tuning fork.No faults with the radar gun system were recorded.The battery operated radar gun was interfaced to a porta-ble computer and was sampled at a rate of 31.25 Hz. Theacquisition of data from the radar gun unit was moder-ated by proprietary software. The raw data were storedfor later analysis.The portable radar acquisition system was concealedentirely within an unmarked vehicle (the “ radar vehicle ” ),with the tinted windows of the vehicle obscuring the radarunit and its operators. Without any visual cue, the radarvehicle was indistinguishable from any typical parkedvehicle.TEST LOCATION AND ENVIRONMENT  –  Decelerationtesting was conducted between September 1995 andJanuary 1998 at various locations within the city of Sur-rey (a suburb of Vancouver), British Columbia, Canada.The data was collected under varying weather conditions(rain, wind, and clear), road surface conditions (wet anddry) and illumination conditions (daylight, dusk and afternightfall). Test sites were chosen that were straight andlevel on the approach to a stop sign; therefore, there wasan unobstructed view of the signage.Stop sign controlled intersections were preferentially cho-sen, based upon geometric and traffic volume con-straints. Streets with multiple lanes in each direction andintersections with active cross traffic were rejected asunsuitable since they permit excessive background trafficto generate extraneous radar data. As the acquisition ofdeceleration data from one vehicle in isolation wasdesired, testing locations with high traffic volume werealso unsuitable because secondary vehicles tended toenter the radar gun ’ s field of view before the primary vehi-cle completed its deceleration.TEST PROCEDURE  –  The radar vehicle was driven to aselected site and parked as close to the edge of the road-way as practicable. The radar vehicle was positioned fac-ing the intersection stop sign in the same direction as thetarget vehicles. The radar unit was mounted in the radarvehicle on a tripod and aimed forward to be approxi-mately parallel to the roadway. The calibration of theradar gun and the functionality of the control softwarewere verified prior to the commencement of testing.During testing, target vehicles were identified as theyapproached and passed the radar vehicle from behind.After the subject passed the radar vehicle, the radar sys-tem recorded the speed of the decelerating target vehicleas it approached the stop sign.Operation of the radar system required two persons. Oneperson was responsible for operating the radar monitor-ing system and pre-processing the acquired data; thispre-processing included truncating the data set or reject-ing the run if it was unusable. The otherwise uncondi-tioned data were saved for later processing. The secondperson observed the approaching vehicles and ascer-tained when a suitable vehicle target was approaching. Atarget was selected if it was sufficiently separated fromother vehicles that it could be independently tracked. Thesecondary role of the observer was to identify the make,model and approximate model year of each recordedvehicle and classify it into one of the following categories:passenger automobiles, minivans, pickup trucks/sportutility vehicles (SUVs), tractor/trailers, sports cars, buses,vans and commercial trucks. Sport utility vehicles are cat-egorized with pick-up trucks as they are built on similarplatforms and have similar performance specifications.The “ sports car ” category reflects vehicles that are mar-keted for their performance: Ford Mustang, ChevroletCamaro, Dodge Viper, Toyota MR2, Mazda RX7, etc.DATA COLLECTED  –  Upon acquisition, a plot of a vehi-cle ’ s deceleration history was immediately generated onthe portable computer (see Appendix A for a sample rawdata plot); the quality of the data and the usable durationof the recorded event were assessed from this plot. Dataruns were immediately rejected if the data was fatallycontaminated by extraneous data, if the usable samplingduration was inadequate, or if the subject vehiclebehaved uncharacteristically. Examples of uncharacteris-tic behavior include those vehicles that did not apprecia-bly decelerate for the stop sign (i.e. did not attempt tostop), and those vehicles that were initially traveling atspeeds that were abnormally distant from the municipalspeed limit of 50 km/h.Deceleration data were recorded for a total of 313 vehi-cles. The vehicles were classified into motor vehicle typebased upon the make, model and estimated vintage. Theoccurrences of each type of vehicle are summarized inTable 1.
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