Felix H. Walz

N km : a proposal for a neck protection criterion for low-speed rear-end impacts

Soft tissue neck injuries sustained in low speed rear-end collisions are of continued concern in road traffic. To assess the risk of sustaining such injuries, various neck injury criteria have been proposed. In this study a new candidate for such an injury predictor called N km was developed. It is based on a linear combination of shear forces acting in the sagittal direction and extension/flexion bending moments, both measured at the occipital condyles. Results from a total of 40 sled tests, all performed using the same test procedure, with various car front seat models, and using a Hybrid III/TRID as well as a BioRID dummy, were evaluated in order to validate the new criterion. Additionally, a mathematical model was set up to determine the behavior of the N km at a higher crash pulse than the one used in the sled tests. It was shown that the new criterion offers the additional possibility to assess the kinematic phase of forward motion. Furthermore, the influence of the seat design on its protective potential could be related to the N km values obtained and thus, the new criterion is eligible to be part of a standard seat test procedure.

SPEED LIMIT REDUCTION FROM 60 TO 50 KM/H AND PEDESTRIAN INJURIES

Impact speed is the major parameter for the causation of pedestrian injuries. After the introduction of a 50 km/h speed limit, reduced from 60 km/h in the city of Zurich, the incidence of car-pedestrian accidents was cut by 16%, the number of injured pedestrians by 20%, and the fatalities by 25%. These are results of an investigation of a complete sample of 946 car-pedestrian accidents in Zurich during two years, one before and one after the introduction of the lower speed limit. The most pronounced reduction was seen with victims rated MAIS 5 (decline of 86%). A detailed analysis of the ISS categories is given in terms of mortality and survival time. Fractures of the ribs and the pelvis were reduced by 50%. Special attention is given to impact speed. Due to a 36% lower overall hospital related treatment period the medical expenses were cut considerably. The analysis revealed that virtually the whole reduction should be attributed to the lower speed limit and not to other parameters such as the number of inhabitants or cars registered, cost of gas, etc. For the covering abstract of the conference see HS-036 716. (Author/TRRL)

Compatibility considerations for low-mass rigid-belt vehicles.

A number of staged impacts performed by our group with the aid of a test device representing a low-mass vehicle (LMV) indicates that a rigid-belt body (RBB) is a valid means for providing adequate occupant safety also for LMVs in the strict sense (curb mass less than 600 kg). The RBB concept raises the problem of compatibility, however. Ideally, the deformability of car front structures should increase with increasing vehicle weight in order to ascertain compatibility. Published data on frontal deformation characteristics substantiate in contrast that conventional cars today exhibit an opposite behaviour. To evaluate the compatibility properties of ultrastiff LMVs, two crash experiments were performed along with a theoretical model analysis. An LMV with a mass of 680 kg (including batteries, 50% mass of two dummies, instrumentation) designed according to the RBB concept and a conventional care of 1320 kg--(equivalent loading conditions as LMV)--were crashed at 56 km/h in a frontal direction against a deformable barrier (FMVSS 214). Furthermore, a mathematical model was based on estimated deformation characteristics of conventional vehicles to predict intrusion distances into the FMVSS barrier in hypothetical frontal crashes with 56 km/h. The results indicate that due to its low mass an LMV does not represent an excessive compatibility problem for other car occupants in spite of the stiff RBB characteristics.

EJECTION AND SAFETY BELTS

Abstract In 1976 the Swiss Federal Department of Justice and Police initiated a one year study of injured seat belt wearers. The data of the 410 OAIS ⩾ 2 cases registered are here analysed with regard to the 15 occupants ejected despite belts. Ejection turned out to be the most traumatic accident situation in terms of mean ISS and death rate. The injuries sustained by the ejected occupants are discussed. The main reason for ejection was slipping out of two point shoulder belts in rollovers, followed by torn three-point belts.

Frequency and significance of seat belt induced neck injuries in lateral collisions

It is well established that properly worn seat belts reduce the incidence of severe neck injuries in car accidents in general. However, for certain configurations of nearside lateral collisions this statement has not been substantiated beyond any doubt by the published field accident data. In order to further evaluate this question, the samples of two accident investigation programs, one from Switzerland and one from France, were combined and analysed accordingly. They contain a total of 810 wearers of three point belts, 98 of which are cases of lateral nearside impacts. In 10% (N equals 10) of this subset neck injuries of AIS greater than or equal to 1 were registered. 7 of those 10 cases were of a degree of AIS greater than or equal to 2 whereby 2 of them could directly be attributed to an immediate belt contact. The corresponding incidence of neck injuries in the rest of the sample (712 cases of frontal, farside impacts, rollovers etc. with 111 victims exhibiting a neck injury rated AIS greater than or equal to 1) is not significantly different.