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Simms C.K.,Trinity College Dublin | Wood D.,Denis Wood Associates | Fredriksson R.,Autoliv
Accidental Injury: Biomechanics and Prevention | Year: 2015

Pedestrians account for about one third of road accident fatalities worldwide, but there are large regional variations. In general, in highly motorized countries pedestrians account for around 10-20 % of fatalities, but in less motorized countries, pedestrians can account for over 50 % of fatalities. Pedestrians are frequently classed as vulnerable road users as they have a higher fatality rate than vehicle occupants. Protecting pedestrians from vehicle collisions requires a combination of road engineering, vehicle design, legislation/enforcement and accident avoidance technology. The separation of pedestrians from fast-moving motorized vehicles is preferable and pre-crash sensing methods combined with autonomous braking technology can greatly reduce the occurrence and severity of pedestrian accidents. However, these approaches cannot prevent all accidents, and vehicle/pedestrian collisions remain a real and frequent problem.Pedestrian kinematics during the vehicle contact phase are strongly correlated to the vehicle speed and the height of the vehicle front-end structures relative to the pedestrian height. However, the subsequent ground contact is a highly variable event, which nonetheless accounts for a significant proportion of head injuries.Vehicle impact speed is the main determinant in pedestrian injury outcome. However, despite a popular view that pedestrian safety cannot be significantly improved due to the mass and stiffness disparity between unprotected humans and motorized vehicles, it is now well established that vehicle design has a significant effect on the severity and distribution of pedestrian injuries arising from vehicle impact. In particular, the height of the bonnet leading-edge relative to the pedestrian’s centre of gravity is significant for the kinematics and subsequent injuries, and the stiffness of the main contact surfaces on the vehicle also plays a significant role.Many modern cars feature active pedestrian safety devices such as warnings, autonomous braking, external airbags and pop-up hoods. In the future, the combination of improved vehicle shapes with reduced critical stiffness and auto-braking technology are likely to yield further substantial decreases in pedestrian injuries and fatalities. © Springer Science+Business Media New York 2015.

Wood D.P.,Denis Wood Associates | Elliott J.R.,Trinity College Dublin | Lyons M.,Trinity College Dublin | Augy S.,Trinity College Dublin | Simms C.K.,Trinity College Dublin
International Journal of Crashworthiness | Year: 2013

Road traffic injuries could become the fifth leading cause of death globally by 2030 unless appropriate countermeasures are taken. Reliable reconstruction of collisions is a prerequisite for this, and determination of vehicle impact speed is the critical reconstruction parameter for vehicle-pedestrian collisions. In this paper, a validated Constant Inertial Property pedestrian model is applied in a Monte Carlo simulation environment to assess the feasibility of using pedestrian wrap-around ratio in the estimation of vehicle impact speed for collision scenarios involving a range of pedestrian pre-impact gait positions, anthropometrics, vehicle shapes and braking conditions for wrap type pedestrian impacts. The results show that there is a clearly identifiable increase in wrap-around ratio with vehicle impact speed up to a speed in the region of 40 km/h, after which further increases in impact speed produce very little change in wrap-around ratio. This characteristic is confirmed from fundamental impact and kinematic analysis. Therefore, the results show that for higher-speed cases only minimum speed predictions may generally be reliable. Statistical analyses of the Monte Carlo simulation results are then used to provide Confidence Limits and Odds Tables for accident reconstruction purposes. These provide the first quantitative approach to vehicle speed prediction from pedestrian wrap-around ratio. © 2013 Taylor & Francis Group, LLC.

Elliott J.R.,Trinity College Dublin | Augy S.,Trinity College Dublin | Simms C.K.,Trinity College Dublin | Wood D.P.,Denis Wood Associates
International Research Council on the Biomechanics of Injury - 2010 International IRCOBI Conference on the Biomechanics of Injury, Proceedings | Year: 2010

For vehicle-pedestrian accidents, knowledge of pedestrian pre-impact speed aids in understanding post-impact kinematics, injury patterns and legal culpability. It is hypothesised that the transverse offset between the primary and secondary impact locations on the vehicle, which is often measureable from vehicle damage patterns, can be used to deduce pedestrian pre-impact speed. Following validation, a statistical tool based on a Constant Inertial Property (CIP) pedestrian model was used to evaluate this hypothesis. Results show that limits of pedestrian pre-impact speed can be predicted based on the transverse offset, if independent estimates of vehicle impact speed and possibly pedestrian stance are available.

Elliott J.R.,Trinity College Dublin | Simms C.K.,Trinity College Dublin | Wood D.P.,Denis Wood Associates
Accident Analysis and Prevention | Year: 2012

In road traffic collisions, pedestrian injuries and fatalities account for approximately 11% and 20% of casualties in the USA and the EU, respectively. In many less motorised countries, the majority of victims are pedestrians. The significant influences of vehicle speed, pedestrian speed and pedestrian gait on pedestrian post-impact kinematics have been qualitatively noted in the literature, but there has been no quantitative approach to this problem. In this paper, the MADYMO MultiBody (MB) pedestrian model is used to analyse the influences of vehicle speed, pedestrian speed and pedestrian gait on the transverse translation of the pedestrian's head, head rotation about the vertical head axis and head impact velocity. Transverse translation has implications for injury severity because of variations in local vehicle stiffness. Head rotation is related to pedestrian stance at impact, which is known to affect the kinematics of a collision. Increased head impact velocity results in greater head injury severity. The results show that transverse translation of the head relative to the primary contact location of the pedestrian on the vehicle decreases with increasing vehicle speed and increases linearly with increasing pedestrian speed. Head rotation decreases with increasing vehicle speed and increases linearly with increasing pedestrian speed, but these variations are small. The range of head rotation values decreases with increasing vehicle speed. Head impact velocity increases linearly with vehicle speed and is largely independent of pedestrian speed. Transverse translation, head rotation and head impact velocity all vary cyclically with gait in clearly definable patterns. © 2011 Elsevier Ltd. All rights reserved.

Nishimura N.,Trinity College Dublin | Nishimura N.,Meijo University | Simms C.K.,Trinity College Dublin | Wood D.P.,Denis Wood Associates
Accident Analysis and Prevention | Year: 2015

Abstract Rear impact collisions are mostly low severity, but carry a very high societal cost due to reported symptoms of whiplash and related soft tissue injuries. Given the difficulty in physiological measurement of damage in whiplash patients, there is a significant need to assess rear impact severity on the basis of vehicle damage. This paper presents fundamental impact equations on the basis of an equivalent single vehicle to rigid barrier collision in order to predict relationships between impact speed, maximum dynamic crush, mean and peak acceleration, time to common velocity and vehicle stiffness. These are then applied in regression analysis of published staged low speed rear impact tests. The equivalent mean and peak accelerations are linear functions of the collision closing speed, while the time to common velocity is independent of the collision closing speed. Furthermore, the time to common velocity can be used as a surrogate measure of the normalized vehicle stiffness, which provides opportunity for future accident reconstruction. © 2015 Elsevier Ltd. All rights reserved.

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