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This paper examines the dynamic displacement-crushing force and dynamic displacement-absorbed energy behaviour of eight cars in full width barrier, 45% overlap rigid barrier and 30° angled barrier tests at 56, 50 and 56 kph respectively. This study shows the frontal crush behaviour of these cars can be divided into three regions or zones of constant force, these zones being associated with crushing of the front structure as far as the engine, the engine and rear front structure and the occupant compartment. The highest average crushing force is associated with crushing of the engine and rear front structure with lower average crushing forces required for the extreme front of the car and for the occupant compartment. It is hypothesised that the energy absorbed-dynamic displacement behaviour in the full width barrier test represents the energy absorbed-mean displacement for all other crush configurations.

In temperate climatic conditions the water depths on wet roads are generally low, typically less than 1 mm. In this paper we examine the various types of road surface and the manner in which they can be classified in terms of macro and micro-texture. We propose a simplified representation of the tyre road interface in which the tyre footprint is divided into two zones, a dry zone in which dry road friction levels are obtained and an initial wet zone in which there is a water layer between the tyre and road and which gives no retardation. A generalised relation for the variation in the size of the wet zone with speed is proposed. The model is applied to published data for road surfaces of differing characteristics with fully treaded and smooth tyres. The model is shown to give a good representation of the variation in locked wheel retardation with speed and highlights the sensitivity of stopping distance to variations in road surface and tyre tread depth.

This paper provides a theoretical explanation for the reported car size effect in frontal collisions. The frontal crush behaviour of the car population is examined arid shows that the specific energy absorption per unit mass propel-ties of the car population are independent of car size. Examination of single car crashes and car to car collisions in this context shows that the mean deceleration experienced by a car is inversely proportional to car length, is related to the square root of the collision closing speed arid to the inverse of the fourth I-oot of mass ratio and of crush depth. It is hypottiesised based on the Gadd severity index, for any specific car population and given degree of occupant protection within this population that Relative Injury Risk is proportional to the 2.3 power of mean deceleration.

This paper examines the deformation patterns of car fronts involved in both narrow object and offset frontal collisions and shows that the car side or sides not involved in direct crushing are pulled towards the centre of the car about a hinge point located 0.32 of the overall length to the rear of the front of the car. This corresponds with the location of the front of the car door/front bulkhead. The resulting crush profiles can be represented by simple geometric shapes. These are combined with a previously derived Specific Energy Absorption representation for the overall car population and applied to narrow object and pole impacts with car fronts. When compared with 19 staged pole impacts carried out by NHTSA high correlation is obtained and it is shown that the 95% confidence limits for calculated speed is +/- 9 km/hr.