Motorcycle Accident Reconstruction Part I - Physical Models

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1 Motoryle Aident Reonstrution Part I - Physial Models Oren Masory Wade Bartlett Bill Wright Dept. of Oean & Mehanial Engr. Mehanial Forensis Engineering Servies IPTM Florida Atlanti University 179 Cross Road th Street North Boa Raton, FL Rohester NH West Pal Beah, Fl asoryo@fau.edu wade.bartlett@gail.o bwright@tarorigin.o ABSTRACT The purpose of this paper is to evaluate different forulas whih are used to estiate the otoryle s pre-ollision speed in otoryle-to-ar aidents. These forulas are based on easurable physial paraeters suh as otoryle wheelbase hange and fundaental physial laws suh as onservation of oentu. The evaluation used data fro rash experients perfored by the authors as well as published experiental data. The results of these evaluations indiate that the otoryle s pre-ollision speed annot be estiated with high auray. Keywords Motoryle Aidents, Motoryle Aidents Reonstrution, Vehile Aidents. 1. INTRODUCTION Aording to the National Highway Traffi Safety Adinistration (NHTSA), in 1969, there were 2.3 illion otoryles registered in the United States. This nuber inreased draatially during the next 40 years and urrently there are over seven illion otoryles registered in the United States. Obviously, as the nuber of otoryles on the road inreased, so did the aident rate. In 1969, there were 69,500 otoryle aidents reported, in whih 1,855 persons were killed. In 2004, 4,008 otorylists were killed in the US, an 8% inrease fro The death rate per 100 illion vehile iles traveled for a otorylist is over 35 ties higher than of an autoobile oupant [1]. One of the ain and unequivoal reasons otorylists are killed in rashes is beause the otoryle itself provides virtually no protetion in a rash. For exaple, approxiately 80 perent of reported otoryle rashes result in injury or death while a oparable figure for autoobiles is about 20 perent. The earliest and the ost frequently ited testing was published by Severy in 1970 [2], whih inluded one test at 20ph, one test at 40ph, and 5 tests at 30ph. That paper inluded a hart showing a linear relationship between wheelbase redution and speed with high orrelation fator of The Severy data is not relevant to today's otoryles: hassis design, wheels, aterials, engine ounting, and front end suspension styles have hanged enough that his data is not appliable. In 1976, Professor Harry Hurt [3] of the University of Southern California onduted a study of 3,600 otoryle aidents in the Los Angeles area. The results of this study have beoe the basis for uh otoryle rider training and researh. The study found that in 65 perent of the ulti-vehile ases the autoobile violated the otoryle right of way. A siilar survey onduted by the Philadelphia polie Departent showed that suh a violation is the ause in only 45 perent of all otoryle aidents in the ity of Philadelphia. Hurt s study also found that in 64 perent of single-vehile otoryle aidents, the operator was responsible for his aident. The ajority of aidents ourred on a lear, dry day during daylight hours and typially, the otoryle operator had less than six onths riding experiene and no foral training. For any years there has been soe ontroversy over the use of onservation of linear oentu to estiate the speed of otoryles involved in ollisions with other otor vehiles. Frike and Riley stated in [4] that oasionally a oentu analysis is attepted and that this tehnique rarely works well in aurately estiating the speed of the otoryle. They explained that the heading and departure angles beoe sensitive when the angles of approah are nearly ollinear and the weight differene between the olliding vehiles is fairly large. In 1990, Brown and Obenski write that a oentu analysis an soeties be used in otoryle aidents, and give a graphial exaple of a oentu vetor diagra of a otoryle/autoobile ollision. [5] In 1994, Obenski [6] further larified this position by stating Generally it is triky to use oentu analysis in aidents between vehiles with a big weight differene, but gives the sae graphial exaple as in his previous work. Obenski speifially autioned against using a oentu analysis where the autoobile has been oved very little after ipat with the otoryle. In 1990, Niederer [7] wrote about tehniques that ay be used to reonstrut otoryle/vehile ollisions, with the ephasis of the paper on the use of onservation of linear and angular oentu. Niederer speifially autioned that due to the often unfavorable ass ratio an aurate reonstrution ay be ipeded, but onluded that when used autiously, the use of oentu and other available inforation represents a powerful tool for otoryle-vehile ollision reonstrution. He further onluded that reonstrutionists should assess the sensitivity of the oentu analysis to hanges in variation of ipat onfiguration and post ipat trajetory. 1

2 In [8] the priniples of linear and angular oentu onservation were investigated. It was onluded that Use of the sensitivity analysis will allow the reonstrutionist to deterine if the tehniques should be applied to the given analysis or be abandoned in favor of other ethods of speed analysis. In [9], the validity of 10 different relationships, whih are to evaluate a otoryle s pre-ollision speed strikes a passenger ar, were evaluated. In ontrary to expetations, the orrelations between speed and rush were always stronger than any relations involving energy. When onteplating speed-fro otorylerush, it has been oonly assued that that the type of wheel, ast or spiked, was an iportant onsideration. This analysis showed that while wheel type does affet the otoryle-to-ar rush ratio, the total rush was not signifiantly affeted. The equations that ost aurately predited the reported ipat speed of the test otoryles were the Eubanks-for equations, with the odifiations suggested by this analysis that aount for the differenes between the door/fender ipat areas and the pillar/axle areas. The door/fender ollision speeds were found to be predited with a 95% onfidene range of plus or inus 20% of the noinally alulated value, while the pillar/axle speeds were predited within a range of plus or inus 28%. Fro aident reonstrution point of view there is a liited aount of data, opared with vehile ollision data whih akes aurate odeling very diffiult. Collision tests involving ars oving at high enough speeds to affet the otoryle s trajetory are very rear. In these ases it appears to redue the total easured rush, suh that using the relationships developed here will under predit speeds, typially by 15%. The additional opliation of a oving target vehile also inreases the data spread signifiantly. The liited ar-buper ipat testing appeared to be very siilar in rush harateristis to the pillar/axle ipats, but the data set was too sall for signifiant analysis. This paper provides analysis of test results of 13 different tests in whih the otoryles were rushed into the side of a ar. The ipat veloity ranged fro 40-58[ph] and the ipat point on the ar varied. The otoryle s wheelbase hange, width and the axiu indentation and the oveent of the vehile were reorded. In addition, data fro previous 56 tests were used to hek the analysis results. Figure 1: Photos of soe of the otoryle Figure 2: Data olleted for eah test. 1. CRASH TESTS Sixteen otoryles were used in the rash-tests. Figure 1 shows soe photos these otoryles. The data olleted for eah test is shown in Figure 2. The inforation on eah otoryle is given in App. I. 2. DATA ANALYSIS 2.1 Model I Wheelbase redution In this odel the pre-ipat speed of the otoryle is orrelated with the wheelbase redution. This odel is the earliest odel, proposed by Severy. The wheelbase redution data of the previous 56 tests were graphed versus the pre-ipat speed as shown in Figure 3. As shown the data is sattered and does not fit a straight line sine orrelation fator 0.27 whih indiates a poor orrelation. Wheelbase Redutuin [in] y = x R 2 = Motoryle Ipat Speed [ph] Figure 3: Results of odel I. 2

3 2.2 Model II Total rush With this ethod the otoryle speed is orrelated with the Total Crush whih is the soe of the otoryle s wheelbase redution and the axiu indentation of the vehile s rush. The orrelation, if exists, eliinates the need of knowing the stiffness of the otoryle struture as well as the loal stiffness of the vehile at the ipat loation. However, two different ases are being onsidered: 1) The otoryle strikes vehile at a soft loation suh as a door or a fender; and 2) A hard point is being struk suh as a pillar or within 3 inhes of an axle. For the first ase the following linear relationship with a orrelation fator of 0.8 was obtained (see Figure 4): where: 70 V (1) = 1.43( L + C) V Motoryle ipat speed (ph) L Motoryle wheelbase redution (inhes) C - Maxiu indentation in the vehile s rush zone (inhes) As shown in Figure 7, the only good orrelation is when the ipat loation is around the axle, probably beause the stiffness at this point is very high for every vehile. Motoryle Ipat Speed (ph) y = 1,5875x + 14,72 R² = 0, Cobined Crush (inhes) Figure 5: Motoryle speed estiate Hard loation Speed Estiation Error [%] - Ipat at Axle 30% 60 20% Motoryle Ipat Speed (ph) y = 1,426x + 10,403 R² = 0,8072 Error (in perentage) 10% 0% % -20% 10-30% Cobined Crush (inhes) -40% Atual Speed [ph] Figure 4: Motoryle speed estiate Soft loation Figure 6: Motoryle speed estiation error where ipat at the axle. Siilarly, for ipats at hard The following relationship with a orrelation fator of 0.76 was obtained (see Figure 5): V (2) = 1.59( L + C) % 25% 20% Speed Estiation Error [%] - Opat at Pilar Using the odel, pre-ollision speed of the otoryle was estiated. The estiation errors are illustrated in Figure 6 through 8 for different ipat loation on the ar. As shown, in ases where the ipat loation is hard (pillar or axle) the largest estiation errors are approxiately 30% while when the ipat loation is soft the error reah 40%. In both ases, the results are not aeptable. The data was separated aording to the loation of the ipat: 1) Fenders and door; 2) Pillar ±3 inhes; and 3) Axle ±3 inhes. The reason behind this lassifiation is the differene in the stiffness at these loations. The results are shown in Figure 7. Error (in perentage) 15% 10% 5% 0% -5% -10% Atual Speed [ph] Figure 7: Motoryle speed estiation error where ipat at the pillar. 3

4 50% Speed Estiation Error [%] - Ipat at Door The sae way the post ipat of the vehile an be alulated. Error (in perentage) 40% 30% 20% 10% V 2 gl = µ (5) Where: L - Vehile s skid arks length µ - Coeffiient of frition between the vehile and the skidding surfae 0% -10% Using onservation of linear oentu priniple, the preipat speed of the otoryle an be found by: Atual Speed [ph] Figure 8: Motoryle speed estiation error where ipat at the door. V ( M µ L + M µ l ) g = 2 (6) M 2.3 Model III Conservation of linear oentu The Law of Conservation of Moentu ditates that the total oentu just prior to two eleents olliding is the sae as the total oentu just after the ollision. In ost otoryle ollisions this basi forula ust be expanded to inlude both otoryle and rider post-ipat veloity, sine the otoryle and rider seldo stay together following the ollision. This relationship is given by: ( M + M r ) V = M V + M V + M rvr (2) where: M - Motoryle s ass M r - Rider s ass M - Vehile s ass V - Vehile s post ipat speed V - Motoryle s post ipat speed V r - Rider s post ipat speed As shown in Figure 9, the use of the priniple of linear onservation priniple yields poor results with soe ases where the estiation errors exeeding 100%. It is interesting to note that all errors are negative whih eans that the odel overestiate the atual speed. In test onditions Eq. 2 is siplified in this ase sine there was no rider on the bike, M V + = M V M V (3) To estiate post ipat speed of the otoryle onservation of energy relationship is used: V 2 gl = µ (4) Where: g - Gravitational aeleration l - Motoryle s skid arks length µ - Coeffiient of frition between the otoryle and the skidding surfae Figure 9: Estiation errors of the pre-ipat otoryle speed using linear oentu onservation. 2.5 Model IV Conservation of Angular oentu The MNally Rotational Moentu Method [8] utilizes vehile inforation (weights, weight distributions, ipat loation, vehile rotation), and sene inforation (post ipat speed and diretion of both vehiles). The first step in the rotational analysis is to deterine the total aount of torque ating through the tires/roadway interation to slow the angular veloity of the vehile following the ollision. 4

5 In side ollisions the ipulse applied to the vehile results in the struk end of the vehile sliding, while the opposite end ats a pivot point. When this type of vehiular otion ours, it is possible to alulate the torque ating on the vehile by: τ = M gw µ (7) tire b where: τ tire - Torque aused by the tires sliding sideway W b - Vehile s wheelbase The value of torque alulated above an then be used in the following forula, whih alulates the rotational veloity of the vehile. 2τ θ tire ω = (8) 2 I + M d where: ω - Angular veloity of the vehile θ - Vehile s angle of rotation I - Yaw oent of inertia d - Distane of the farthest axle fro the ipat point to the enter of gravity of the vehile At this point the hange in the otoryle speed, due to the ipat, an be deterined: Figure 10: Estiation errors of the pre-ipat otoryle speed using angular oentu onservation. 3. CONCLUSIONS The paper desribes 5 different ethods, by whih the preipat speed of a otoryle during a ollision with the side of a vehile, an be estiated. While the oentu onservation ethods are based on priniples on ehanis, their estiate of is very poor. Out of the other 3 ethods only the obined rush ethod produed good results. Fro aident reonstrution point of you, these are enouraging results sine in any ases the inforation available is very liited. For exaple, in any ases the aident site went through hanges or soe tie passed sine the aident and as a result skid arks are not available. However, at the best both vehiles are still available for inspetion and the required two paraeters, required for the obined rush ethod, an be easured. ( I + M d )ω 2 V = (9) SM where S is the length of oent ar deterined by easuring the perpendiular distane fro the prinipal diretion of fore to the enter of ass of the vehile. If we know the diretion of travel of the otoryle at ipat and its post-ipat veloity, are know, the ipat speed of the otoryle an be deterined. Figure 10 show the estiation errors of the otoryle s pre-ipat speed. As in the previous ase, the errors are large and reahing 80%. Siilarly, in ost ases the pre-ipat speed is over estiated. 4. REFERENCES [1] [2] Severy, D., Brink, H., and Blaisdell, D., "Motoryle Collision Experients," SAE Tehnial Paper , [3] [1] Motoryle Aident Cause Fators and Identifiation of Countereasures, Volue 1: Tehnial Report, Hurt, H.H., Ouellet, J.V. and Tho, D.R., Traffi Safety Center, University of Southern California, Los Angeles, [4] Frike, Lynn B., and Riley, Warner W., Reonstrution of Motoryle Traffi Aidents, Topi 874 of the Traffi Aident Investigation Manual, Northwestern University Traffi Institute, 1990 [5] Brown, John F., and Obenski, Kenneth S., Forensi Engineering Reonstrution of Aidents, Charles C. Thoas, [6] Obenski, Kenneth S., Motoryle Aident Reonstrution: Understanding Motoryles, Lawyers & Judges Publishing Co.,

6 [7] Niederer, Peter F., Soe Aspets of Motoryle-Vehile Collision Reonstrution, SAE Paper , Soiety of Autootive Engineers, [8] Brue F. MNally, Wade Bartlett, 20th Annual Speial Probles in Traffi Crash Reonstrution at the Institute of Polie Tehnology and Manageent, University of North Florida, Jaksonville, Florida, April 15-19, 2002 [9] Adason, Kelley S.; Alexander, Peter; Robinson, Ed L.; Burkhead, Claude I.; MMannus, John; Anderson, Gregory C.; Aronberg, Ralph; Kinney, J. Rolley; Sallann, David W.; Johnson, Gary M.; Seventeen Motoryle Crash Tests Held at WREX2000, WREX2000 Conferene Results, APPENDIX I Motoryles data 6