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Evaluation of the kinematics and injury potential to different sizes of

pedestrians impacted by a utility vehicle with a frontal guard

Article  in  International Journal of Crashworthiness · December 2011

DOI: 10.1080/13588265.2011.616115

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Evaluation of the kinematics and injury potential todifferent sizes of pedestrians impacted by a utilityvehicle with a frontal guardRasoul Moradi a & Hamid M. Lankarani aa Department of Mechanical Engineering, Wichita State University, Wichita, KS, USA

Available online: 22 Sep 2011

To cite this article: Rasoul Moradi & Hamid M. Lankarani (2011): Evaluation of the kinematics and injury potential todifferent sizes of pedestrians impacted by a utility vehicle with a frontal guard, International Journal of Crashworthiness,16:6, 645-655

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International Journal of CrashworthinessVol. 16, No. 6, December 2011, 645–655

Evaluation of the kinematics and injury potential to different sizes of pedestrians impacted by autility vehicle with a frontal guard

Rasoul Moradi and Hamid M. Lankarani∗

Department of Mechanical Engineering, Wichita State University, Wichita, KS, USA

(Received 13 May 2011; final version received 17 August 2011)

A review of accident data reveals that in most pedestrian accidents, the head and lower extremity injuries are the predominantareas of injury to the pedestrian. The vehicle front geometry profile and stiffness, as well as impact speed are importantfactors governing pedestrian kinematics. Accident data show that the fatality rate for pedestrian/utility vehicle impact isgreater than that for pedestrian/passenger car impact. The addition of a front guard on light trucks and sports utility vehiclesto mitigate damage during off-road activity, or to provide mounting points for extra lights, makes the pedestrian morevulnerable to the impact. In this study, a computational technique is utilised to quantify the influence of the added frontguard on the impacted pedestrian. A computer-aided design model of a typical commercial frontal guard is developed, andthe finite element analysis, along with impact test, is conducted to obtain the stiffness properties of the guard. Differentsizes of pedestrian models in the MADYMO code are utilised, and the validated facet-surface model of a pickup truck isused to generate a vehicle front surface. The entire model is validated by comparing the pedestrian kinematics and injuryparameters with the published data. This study demonstrates that for all sizes of pedestrians, the mid-body region is morevulnerable when a guard is added to the vehicle. The results from this study can be utilised in the designing of front guards,the frontal crash zone of utility vehicles and installation of these aftermarket guards in order to protect vulnerable roadusers.

Keywords: pedestrian safety; frontal guard; light trucks and vans (LTV); pedestrian kinematics; injury potential

Introduction

Statistical data have indicated the vulnerability of pedes-trians and cyclists when impacting a motor vehicle inurban areas. In 2009, pedestrians accounted for 12%of all highway fatalities in the United States [32].In 2005, 8.7% of vehicle–pedestrian impacts in theUnited States were fatal, whereas the corresponding fa-tality rate for occupants in vehicle crashes was 1.3%(http://www-nrd.nhtsa.dot.gov/Pubs/TSF2005.pdf; 2005).The Fatality Analysis Reporting System (FARS) databaseon pedestrian fatalities shows that light trucks and vans(LTVs) are the major source of pedestrian death (www-fars.nhtsa.dot.gov/People/PeoplePedestrians.aspx; 2008).This difference can be attributed to the different sizes,shapes, and stiffness of LTVs when compared with pas-senger cars. The analysis of real-world crash data in theUnited States indicate that 11.5% of pedestrians struck bylarger sport utility vehicles are killed, compared with 4.5%of pedestrians struck by passenger cars [14].

In the last two decades, the on-road fleet in the UnitedStates has experienced a nearly 200% increase in the num-ber of LTVs [6,19,22]. In general, these vehicles impactmore aggressively than passenger cars [6], which have

∗Corresponding author. Email: hamid.lankarani@wichita.edu

led to greater concerns about pedestrian safety when theyare involved in impacts. Data indicate that the size ofthe pedestrian and the vehicle frontal area are the dom-inant factors in injury outcomes. Hence, design innova-tions to the front of the vehicle are sought to mitigateimpact loads on the pedestrian (www-fars.nhtsa.dot.gov/People/PeoplePedestrians.aspx; 2008) [2]. It has beendemonstrated that the shape of a sports utility vehicle’s(SUV) frontal structure is a factor resulting in higher pedes-trian injuries to the mid-body region as compared withthe shape of passenger cars. In pedestrian–SUV impacts,the pedestrian is struck more centrally with respect to thebody’s centre of gravity (CG), increasing the momentumtransfer in the primary impact [28]. This clearly indicatesthe higher aggressiveness of SUVs than passenger cars to-wards pedestrians [1,14,15,24]. Car manufacturers addressthe mitigation of injuries to pedestrians by distinguishingthe frontal crush area of the vehicle based on the probabil-ity of impacting a pedestrian in the frontal region [11,26].Protection of pedestrians has recently attracted increasedattention because of regulations implemented or proposedin Europe, Korea, and Japan [5,35]. Pedestrian regulations,such as Global Technical Regulations (GTRs), have also

ISSN: 1358-8265 print / ISSN: 1754-2111 onlineC© 2011 Taylor & Francis

http://dx.doi.org/10.1080/13588265.2011.616115http://www.tandfonline.com

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been developed since 1987 as a part of efforts to increasepedestrian safety [3,4,10,30].

Many consumers of pick-up trucks and SUVs purchaseand attach frontal guards to their vehicles. The main purposeof the guard is to deflect brush and other vegetation fromfragile vehicle parts in order to mitigate damage during off-road activity. However, use of these guards is alarminglyhigh in urban areas where they are typically purchased forcosmetic purposes and styling of LTVs. The presence ofa guard significantly changes the vehicle’s front-end dy-namic crash-energy dissipation characteristics from thosein the original design [19]. The most important consider-ation of a retrofitted guard in LTVs is in the alteration ofcrash response and crash-energy dissipating area, as wellas change of the original equipment manufacturer (OEM)-designed and tested crash-zone specification for pedestriansstruck by these vehicles.

Pedestrian kinematics is highly influenced by vehiclefront-end geometry and pedestrian anthropometry. Fur-thermore, a stiff guard on the front of a vehicle signif-icantly affects pedestrian kinematics at any given speed[21]. Vehicle front-end geometry and stiffness character-istics along with pedestrian size and pre-impact configu-ration are important factors determining the injury level[12,13,18,20,23,25,27,29,31]. Moradi et al. [21] found thatLTVs with frontal guards were associated with more thantwo times higher risk of severe pelvis injuries in comparisonwith the originally designed LTVs.

Methodology

In order to investigate the effect of a vehicle front guardon the kinematics of different pedestrian sizes, a computa-tional model was utilised in this study. MADYMO pedes-trian models, namely the six-year-old child, the 50% (mid-size) male and 95% (large-size) male, were impacted witha vehicle front-facet model. The computer-aided design(CAD) model of a typical front guard, consisting mainly oftwo vertical cantilever I-beams and four horizontal tubularbeams, was created, and the finite element (FE) analysisalong with the impact test were conducted to obtain theguard’s stiffness properties. The facet rigid model of a guardwas then fixed rigidly to the front of the vehicle at the ap-propriate location. The overall MADYMO computationalmodel setup consisted of three systems – the road, the ve-hicle, and the pedestrian. Simulations were carried out forvehicle impact speed of 25 km/hr, 36 km/hr, 40 km/hr (forvalidation purposes) and 54 km/hr. All simulations wereexecuted with and without the guard. In 80–90% of cases,a pedestrian crossing the street in urban areas is struck lat-erally by the frontal area of a vehicle at a medium speedof about 40 km/hr [23,8,9,34]; therefore, the model wasdeveloped based on the pedestrian/LTV lateral-impact sce-

Figure 1. (a) Euro NCAP typical pedestrian rating for front-endzone [33]; (b) MADYMO facet model for LTV front-end zone.

nario. To examine the differences between pedestrian mod-els versus a standing dummy model, the results were com-pared with those by Moradi et al. [21]. Pedestrian–ground,pedestrian–vehicle and ground–vehicle friction coefficientsof 0.6, 0.3 and 0.5, respectively, were chosen based on thedata from literature [25,28,33].

LTV modeling

The validated Chevy Silverado FE model from the NationalCrash Analysis Center (NCAC) was utilised in this study.The front region of this model was used to create a facetmodel, which included the bumper, hood, bonnet, fendersand windshield. For the facet model, load-deflection char-acteristics were defined from published results and assignedto various portions of the front end. Figure 1(a) shows thetypical front-end pedestrian rating from the European NewCar Assessment Programme (Euro NCAP) [17]. Figure 1(b)shows the MADYMO facet model of the front-end zones.The load-deflection characteristics of each zone are shownin Figure 2 [17,19,28].

Front-guard modelling

A CAD model of a typical frontal guard used for an LTVwas developed and is shown in Figure 3. The mass of this

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Figure 3. Guard model as used for simulation.

guard is 36 kg, and the design mainly consists of two ver-tical cantilever I-beams and four horizontal tubular beams.The two vertical beams are separated from the centreline bya distance of 700 mm. The horizontal tube was fabricatedfrom a 38.1-mm outer diameter using A-513 grade of steel.The wall thickness is 2.1 mm. The characteristics of the

frontal guard were derived from FE analysis followed bythe experimental test conducted for its validation. Figures4(a, b and c) show the process of FE analysis and the droptest conducted on a front guard and the instrumentationto extract the force–displacement data at different impactvelocities. Figure 4(d) shows the load-deflection character-istic extracted and used for the guard [19]. As observed, theguard has significantly higher stiffness compared with thebumper.

Human models

The validated MADYMO pedestrian models of the six-year-old child, and mid- and large-size males were used in thisstudy, as shown in Figure 5(a) [16]. The initial standing con-figuration of pedestrian models was selected to match thetest conducted by Nierderer and Schumpf [23] and Simmsand Wood [28]. In pedestrian impacts, leg bending and

Figure 4. (a) FE analysis, (b) instrumentation, (c) drop test of guard from temporary drop tower and (d) extraction of load-deflectioncharacteristics used for guard in this study.

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Figure 5. (a) Pedestrian family, from left to right: three-year-old child, six-year-old child, small female, mid-size male and large-sizemale; (b) bending and fracture joints in pedestrian leg [16].

resulting bone fracture are commonly observed. To accountfor this in the pedestrian model, the bending and fractureproperties were implemented at several locations in the fe-mur and tibia using bending/fracture joints, as shown inFigure 5(b) [16]. The large spots show the hip, knee andankle joints, while the small spots show the locations of thebending and/or fracture joints. All fracture joints are spheri-cal joints that are initially locked until a pre-defined fracturetrigger signal exceeds the fracture tolerance level.

Model validation

Validation of the entire LTV/guard/pedestrian model wasconducted by comparing the mid-size pedestrian kinemat-ics with the published results for similar impact conditions.The results from Kerrigan et al. [12], Moradi et al. [21],Niederer et al. [23] and Simms et al. [28] were used for thevalidation of the model in the current study. The compar-ison between the computational model and the published

results shows a reasonably good correlation, as can be seenin Figure 6 for the walking mid-size pedestrian at 40 km/h.Figure 7 shows the validation for the kinematics of bodyparts. Figures 7(a, b) show the head and pelvis CG trajec-tories of a walking mid-size pedestrian when struck by anLTV at 40 km/hr, which shows a fair correlation with the ca-daver or post-mortem human surrogate (PMHS) test resultsfrom [12], as shown in Figures 7(c, d). Figure 8 depictsthe kinematics results from this study and shows reason-ably good correlation with results from the simulation ofa standing dummy laterally impacted by an LTV [21] andexperimental results from PMHS tests [23]. One exceptionis in the lower extremities, which have a greater flexibilityin the MADYMO human pedestrian models but no flexibil-ity in the MADYMO standing dummy models. The greaterflexibility of the lower leg in the human models is due to thefracture joints that are used in them, compared with onlyphysical joints used in the dummy or dummy models.

Figure 6. Walking pedestrian and LTV impact at 40 km/hr. (a) Pedestrian–LTV impact simulation from this study; (b) Pedestrian–SUVsimulation from Simms and Wood [28].

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Figure 7. Head and pelvis CG trajectories of walking pedestrian in vehicle reference system at impact speed of 40 km/hr: (a) and (b)results from this study; (c) and (d) results from Kerrigan et al. [12].

Results

Pedestrian kinematics results

Figure 9 shows the impact of a child pedestrian with an LTVwith and without a guard at an impact speed of 36 km/h. The

impact kinematics for the six-year-old pedestrian is entirelydifferent from those of the mid- and large-size pedestrians,because the translational movement is dominant in this im-pact. The bumper of the original LTV impacts with the

Figure 8. Walking mid-size pedestrian/LTV impact at 25 km/hr. (a) Standing dummy–LTV impact from MADYMO simulation fromMoradi et al. [21]; (b) pedestrian–vehicle with upper leading edge of 90 cm, reconstructed experimentally from PMHS tests by Niedereret al. [23].

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Figure 9. Walking six-year-old pedestrian/LTV impact at 36 km/hr with and without front guard. (a) Child pedestrian/LTV impact withoutguard; (b) child pedestrian/LTV impact with guard.

upper leg and hip of the child pedestrian, followed by thehood edge impacting the head and neck. The pedestrian isthrown away (forward projection) from the car front aftera slight rotation of upper body parts (wrapping behaviour).For an LTV with guard, the pedestrian impact occurs di-rectly with the rigid guard, and the pedestrian forward pro-jection occurs without any wrapping around the car hood.In this case, due to the direct impact of all body parts withthe stiff guard, the rise time of post-impact velocity of bodyparts decreases compared with adult pedestrian impacts andthe LTV without guard impacts.

In the original LTV/mid-size pedestrian side impact,the bumper impacts the pedestrian’s thigh, and after a smallrotation of the pedestrian, the hood edge comes in contactwith the lower torso, elbow and upper arm of the model.The body of the pedestrian gradually rotates and attains ahorizontal position. The kinematics of the mid-size pedes-trian impacting the car involves the entire body translationaland upper body rotational movements. The primary headimpact occurs with the middle area of the hood for the25-km/h impact speed, and then the head slides down thehood. For higher impact velocities of 36 km/h and 54 km/h,the body is thrown ahead of the vehicle, and a significant

rotational movement of the pedestrian is observed, as shownin Figure 10. The secondary impact of the pedestrian’s headwith the ground surface in medium- and high-speed impactsis more severe than the primary impact with the car. Thisscenario changes slightly for an LTV with guard, due to thechange in rotational point and the first contact of the upperleg and pelvis region with the stiff guard. Hence, the headimpact occurs at the frontal part of the hood, which is stifferthan the middle part.

The impact scenario for the large-size pedestrian differsslightly from that of the mid-size pedestrian. The bumperimpacts the pedestrian’s knee and then the hip, and the hoodedge comes in contact with the lower arm. As the bodyrotates and leans against the hood, the head impacts withthe rear part of the car hood, compared with the middle-hood location of the mid-size pedestrian head impact, asdepicted in Figure 11. This results in severe head impact athigh speeds for a vehicle without guard compared with thevehicle that has a guard, whereby the guard causes the bodyto rotate at a higher point, and the head impacts the middlepart of the vehicle hood.

Figure 12 shows the trajectory of the head, upper torsoand pelvis of different pedestrian sizes impacting the LTV

Figure 10. Walking mid-size pedestrian/LTV impact at 36 km/hr with and without guard. (a) Mid-size pedestrian/LTV impact withoutguard; (b) mid-size pedestrian/LTV impact with guard.

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Figure 11. Walking large-size pedestrian/LTV impact at 36 km/hr with and without guard. (a) Large-size pedestrian/LTV impact withoutguard; (b) large-size pedestrian/LTV impact with guard.

with and without a guard. Each trajectory is plotted fromtime t = 0 to a short time after impact. The generic rotationalbehaviour of the upper body parts of different pedestriansizes is depicted in Figure 13, in which the pedestrian isassumed to be a multi-body system articulated at the pointof impact.

Pedestrian injury results

Injury criteria are used to relate physical parameters suchas accelerations and forces to the injuries on human bodyparts. The tolerances and injury criteria are the basis forlegislation and evaluation of injury prevention measures. Avalue of 1000 with a maximum time window size of 36 ms

Figure 12. Head, upper torso and pelvis CG trajectories of different sizes of walking pedestrian/LTV impact without guard (a, b and c,respectively), and pedestrian/LTV impact with guard (d, e and f, respectively) in vehicle reference system at low-speed impact of 25 km/hr.

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Figure 13. After-impact configurations of small- and large-sizepedestrians impacting with LTV with and without front guard.(a) Child pedestrian/LTV impact without guard; (b) child pedes-trian/LTV impact with guard; (c) adult pedestrian/LTV impactwithout guard; (d) adult pedestrian/LTV impact with guard.

is specified for the head injury criteria (HIC), denoted asHIC36, as the concussion tolerance level, which has beenassociated with a 50% risk of skull fracture [7]. The USFederal Motor Vehicle Safety Standard (FMVSS) 208 in-cludes a limit of 700 for HIC, with a maximum window sizeof 15 ms to be a better predictor of head injuries. This limitis denoted as HIC15. The US FMVSS 214 stipulates a peakacceleration tolerance of 130 G for pelvis in a side impact.A commonly stated human tolerance level for severe chestinjury (AIS ≥ 4) is a maximum linear acceleration in the CGof upper thorax of 60 G, sustained for 3 ms or longer based

on FMVSS 208. Thus, the criterion is not based on a singlemaximum value but rather on a sustainable level of linearacceleration. The predicted injuries to a pedestrian’s head,thoracic and pelvis from this study for all impact scenariosare depicted in Figures 14 and 15.

Discussion

The aim of this study was to evaluate the influence of anLTV rigid frontal guard on the kinematics of, and injurypotential to, different sizes of pedestrians. The addition ofa rigid guard on the front of a vehicle amplifies the stiff-ness characteristics of the vehicle’s frontal structure andchanges its front geometry profile. These are the most im-portant factors relative to kinematics and injury potentialto a pedestrian impacted by a vehicle. This change is quan-tified by comparing pedestrians’ kinematics and potentialinjury parameters with and without a guard after impact.

The complete kinematics sequence of the entire impactscenario consists of the pedestrian primary impact (withthe vehicle) and secondary impact (with the ground). Theseverities of these impacts are influenced by the vehicleimpact speed as well as pedestrian size. At the same vehicleimpact speed for a pedestrian, the linear momentum transferfor a six-year-old pedestrian is much more than that for amid- or large-size pedestrian.

The interaction of the LTV and pedestrian is quite dif-ferent from that corresponding to the interaction of a carand pedestrian. In the latter scenario, the pedestrian tendsto rotate and falls on the hood of the car (wrap). The LTV’shigher bonnet height results in direct contact with the mid-region of the pedestrian’s body, which leads to its forwardprojection. This may result in the pelvis being a more vul-nerable body region when impacted by the LTV. This situ-ation is further aggravated due to the presence of the rigidguard in the front of the vehicle. The presence of the guardalters the lead angle of vehicle’s front profile and results in

Figure 14. (a) HIC15; (b) upper torso cumulative 3-ms acceleration in G; (c) pelvis acceleration in G at different LTV impact speeds andfor different sizes of pedestrians–LTV without front guard.

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Figure 15. (a) HIC15; (b) upper torso cumulative 3-ms acceleration in G; (c) pelvis acceleration in G at different LTV impact speeds andfor different sizes of pedestrians–LTV with front guard.

a significant change in the impact kinematics, because theprobability of forward projection is increased. It was ob-served that with the guard, pelvis acceleration increased bymore than two-fold for all pedestrian sizes, as compared tothe case with no guard, which makes the LTV with a guardmore aggressive even at low-speed impacts.

At an impact speed of 25 km/hr or less, the primaryhead contact of the mid-size pedestrian with the vehicle isabsent with and without a guard, and the large-size pedes-trian experiences a very slow touch. In the same situation,the six-year-old pedestrian sustains relatively severe headimpact with the LTV’s front area or rigid guard, far beyondthe acceptable injury level. Addition of the guard increasesthe height of the centre of rotation of the pedestrian’s bodyon vehicle’s front area, and as a result, the head impactoccurs towards the front and middle area of the hood fora mid- and large-size pedestrian, respectively. This resultsin no change or slightly lower HIC value for a large-sizepedestrian, and a slight increase in that of a mid-size pedes-trian at a high-speed impact compared with the same impactscenario without guard.

Torso acceleration is in the safe region for adult pedes-trians for a wide range of impact speeds, but at the sametime, this is beyond the critical level for a six-year-old child,for both LTVs with and without a guard. It was observedthat the thorax injury level for the pedestrian is not signif-icantly influenced by the presence of a guard but mainlydepends proportionally on the impact speed.

When an LTV with or without front guard impacts themid- and large-size pedestrian laterally at low- and medium-impact speeds, the secondary impact of the pedestrian withthe road surface is more life-threatening than the primary

impact with the car in terms of head injury. At low- andmedium-impact speeds, pelvis injury increases with the ad-dition of a frontal guard. At impact speeds greater than40 km/hr, the secondary impact is less important, since theprimary impact with the car front is the first life-threateningimpact. On the other hand, due to the high momentum trans-ferred to the pedestrian at impact speeds of greater than40 km/hr, the addition of a guard is not the dominant life-threatening feature of the high-speed impact. This is entirelydifferent for a small-size pedestrian, who is dominantly in-fluenced by a front guard even at low-speed impacts. For asix-year-old pedestrian, the body and head have less rotationbefore the impact, compared with two other pedestrians. Asa result, the head acceleration in the small-size pedestrian ismuch higher than that for the mid- and large-size pedestri-ans. This is more significant in the presence of a guard, sincethe rise time for head velocity is less than that involving thevehicle without a guard.

Evaluating the after-impact movement of allpedestrian–LTV impacts, Figure 13 depicts the general con-figurations of pedestrian impacts on a vehicle with differentfront-end geometries. Despite some local deformation onboth vehicle and pedestrian, it can be observed that thesmall-size pedestrian is likely to have forward projectionwhen impacted by an LTV with a front guard. When im-pacted by an LTV without a front guard, the small-sizepedestrian behaves as an articulated multi-body having an-gular momentum in the upper body after the first impactwith the bumper. Hence, the head impacts with the car frontat a slightly higher velocity compared with a vehicle withguard. The articulated multi-body impact behaviour canbe observed more for the adult pedestrian compared with

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the child pedestrian, for both front-vehicle configurations.As the angular momentum depends on body dimensionsand moments of inertia, as well as angular velocities, thepedestrian’s upper-body rotation velocity after impact forthe LTV with a guard would be less than that of the LTVwithout a guard. This results in the HIC value being slightlylower for the adult pedestrian when impacted with the LTVwith a guard, compared with that of the original LTV with-out a guard. Hence, in addition to the energy absorptionconsideration, minimising the angular momentum transfercould be utilised in the design of the frontal guard.

Conclusions

A computational model was utilised in this study to inves-tigate the influence of the addition of a vehicle front guardon pedestrian kinematics as a result of impact with theguard. This model was constructed from the FE and multi-body models of the LTV, the guard and the pedestrian. Themodel was then validated using the experimental test andpublished results by demonstrating the correlation betweenthe pedestrian kinematics. The following conclusions canbe made from this study:

• The stiff frontal guard alters the leading angle of thevehicle front profile, resulting in forward projectionof the pedestrian instead of rotation around the hood.

• The influence of the addition of the guard in pedes-trian injury depends on the size of the pedestrian.

• In general, the existence of the front guard increasethe pelvis acceleration by more than 200% for allsizes of pedestrians, and has a low effect on upper-torso acceleration.

• For the small-size pedestrian, the head accelerationincreases catastrophically (about 10-fold) with theaddition of the front guard, but no significant changein the head acceleration was observed for the mid-and large-size pedestrians.

This study clearly demonstrates the poor performanceof LTVs with the addition of a stiff front guard in preventingsevere injury to pedestrians. The presence of a rigid guardon the vehicle front changes the pedestrian kinematics and,due to the high stiffness characteristics of the guard, makesthe pedestrian more vulnerable to injuries, as demonstrated.On the other hand, because the angular momentum of thepedestrian’s upper body is reduced with the addition of afront guard, the relative impact velocity of the upper bodyparts is in turn reduced, and the injury levels in these areas,specifically head injury, may be reduced. Overall, this studydocuments that special attention must be paid to the designand installation of such frontal guards in terms of regula-tions to attenuate the potential injury to pedestrians. Theaddition of compliance tests for the manufacturers of thesefront guards is also recommended. Furthermore, consumersmust be informed of the potential dangers of utilising theseguards.

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