A study was conducted by selecting cases from available NCSS/NASS data on nearside crashes involving fatal chest and abdominal injury. Twenty-five cases indicated overinvolvement of older front-seat occupants in multi-vehicle side impact crashes (76% > 50 years old and 28% > 70 years old). Analysis of the 1975-86 FARS confirmed that older occupants are over-represented in nearside crashes with an incidence of 64% >50 years old and 36% >70 years (as compared to 26% >50 and 8% >70 respectively for single vehicle frontal crashes). The 1982-86 NASS indicare rhar 42% of the seriously injured front seat occupants over 40 years old were in nearside multi-vehicle crashes. This is nearly twice the proportion for younger occupants.

The individual case study also showed that 88% of the multi-vehicle nearside crashes were at intersections and that the driver of the struck vehicle frequently caused the crash by driving error (52%) or traffic violation (17%). The majority of the cases occurred in daylight hours and on dry roads. Alcohol use was not a factor. Changes in visual perception, judgment and attention in the older driver may be factors in crash causation. In addition, a reduced tolerance to impact force probably contributes to injury causation. In terms of automotive design, improvements in side interior padding should aim at safety of older occupants because of their high involvement in this crash type. The analysis raises further questions about the validity of the NHTSA proposed test dummy and injury criterion (SID and TTI) because the dummy develops high, nonhuman-like forces and the injury criterion is sensitive to both protective and unprotective padding. The combination would lead to stiff interiors that particularly place older occupants at continued risk in a nearside crash.

Although an analysis of photographs from the side-impact vehicles indicated that 44Vo of the crashes had sidestructure deformation that was similar to that produced in the NHTSA moving deformable barrier test, only 24Vo- 32Vo of the cases actually addressed the proposed dynamic test. The results of this analysis bear on the preliminary regulatory impact analysis of cost benefit in conducting the side-impact dynamic test. In addition, the review supports the concept that improvements in side-impact protection may be better realized by a slower crash test so that softer padding can be designed to reduce the injury risks of older occupants. The development of improved side interior padding further hinges on the use of a human-like crash dummy and a valid injury criterion, such as the Viscous response, that is sensitive to the underlying risks of internal organ and soft tissue injury of occupants.

One of the next frontiers in automotive safety is to improve occupant protection in side-impactc rashesT. he basis for product improvement is an understanding of crash types and interior contacts that result in serious and fatal injury when the vehicle is struck on the side. An understanding of the crash types is important since the roadway characteristics and traffic mix for side-impact crashes determine the deformations of the side of the struck vehicle. When a vehicle is struck on the side by another motor vehicle, the front-end shape of the striking vehicle is important to the side-structure loading and deformation that occurs. The higher front-end shapes and heavier mass of trucks makes them a particularly important cause of side-impact injuries. The relative speed of vehicles crossing at intersections is another factor in side-impact injury.

Given a better understanding of the type of crashes causing side-impact injury, it is also important to understandth e population at risk of crash injury. This generally focuses on the distribution in age of the victims. Next, it is important to develop an understanding of the circumstances of the crash and, in particular, to determine the general categories of "why" the accident occurred. In many cases, human and environmental factors play an important role in crash causation (Viano 1988a) and a better undersranding in multivehicle side-impacts may lead to specific improvements in driver education and in technologies for accident avoidance. In addition, improvements can be made in side-impact protection as a better understanding of the cause and control of human impact injury is developed from in-depth research on crashc haracteristicsa nd injury biomechanics.

Part of the present study involved case evaluation of fatal side-impact crashes involving a nearside occupant experiencing the most severe injury from chest or abdominal contact on the side interior. The cases involve multi-vehicle side-impacts and are important to a critical evaluation of the U.S. Covernment's preliminary regulatory impact analysis. NHTSA (1988) conducted the analysis to support new dynamic side-impact certification requirements for passenger cars. The dynamic test under consideration involves a moving deformable barrier striking the side of a passenger car. This simulates the crash characteristics of a multi-vehicle impact and judges safety from responses of anthropomorphic test devices placed on the struck side of the vehicle.