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Prevention of head injuries to car occupants: an investigation of interior padding options

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Federal Office of Road Safety - Report CR 160

Authors: A. J. McLean, B.N. Fildes, C.N. Kloeden, K.H. Digges, R.W.G. Anderson, V.M. Moore & D. A. Simpson
Performing organisations: NHMRC Road Accident Research Unit, University of Adelaide and Monash University Accident Research Centre

Full report in .pdf format [355KB]

Abstract

Head injuries to car occupants resulting from crashes on Australian roads are a major cause of death and permanent brain damage. This report evaluates the benefits that would be likely to accrue from the use of padding materials to reduce the severity of impacts to the head. A review of the international literature was conducted to examine the range of possible countermeasures, with particular reference to padding the upper interior of the passenger compartment. Three sets of data analyses were then carried out: first, a summary of objects typically struck by the head in a representative sample of crashes; secondly, an examination of actual brain injuries sustained in a sample of crashes, and an assessment of likely outcomes had the objects struck by the head been padded; and finally, a HARM analysis to estimate the cost of head injuries and the likely financial benefits from various countermeasures. Results indicate that there is considerable potential for reducing the severity and consequences of impacts to the head by padding the upper interior of the passenger compartment. The total annual benefit of this measure, in terms of reduced HARM, would be about $123 million, or $154 per car (with a 5% discount rate). However, an even greater level of protection would be provided by the use of protective headwear. The total benefits associated with headwear in the form of a soft shell bicycle helmet were estimated to be $380 million (assuming a fully airbag equipped fleet), or $476 per car ($626 for cars without airbags).

Executive Summary

Head injuries to car occupants in crashes on Australian roads are a major cause of death and permanent brain damage. Preventing impacts to the head and reducing the severity of the head impacts that do occur has the potential to save many lives and to reduce lifelong suffering by brain damaged individuals and those who have to care for them. This report evaluates the benefits that are likely to accrue from the use of padding materials to reduce the severity of the impact to the head.

The report begins with reference to the recent literature on car occupant head injuries. The range of possible head injury countermeasures is then reviewed briefly, with particular reference to padding the upper interior of the passenger compartment. Such padding, or other means of ensuring that the upper interior provides a specified level of head impact protection, will be required on some new cars in the United States in 1998 and all new cars by 2002. If a similar measure were to be adopted in Australia, it would be more than 15 years before half of the cars on the road provided the specified level of head protection. The development of some form of protective headwear, by comparison, would offer the occupants of all cars a way to reduce their risk of sustaining brain damage if involved in a road crash.

An analysis of factors related to head, neck and face injuries to car occupants follows, conducted by the Monash University Accident Research Centre (MUARC). The frequency with which various objects in the car cause injury to these body regions is listed, together with whether or not there was intrusion into the passenger compartment affecting the struck object. The role of contact with objects outside the car is also noted, although ejected occupants who had not been wearing a seat belt are not included in the data set. Drivers frequently sustained head injury from contact inside the vehicle with the steering assembly, door panel, instrument panel, roof and side window. The steering assembly was not a significant factor in head injuries to left front passengers. Contacts with A- and B-pillars and header and side rails were not frequently involved in head injuries to front scat occupants. This was thought to have been due to relatively high seat belt wearing rates.

The next section of the report presents the results of a detailed analysis of factors related to the occurrence of brain injury in three samples of crash involved car occupants studied by the NHMRC Road Accident Research Unit. On a case by case basis, selected characteristics of the injury to the brain are related to characteristics of the impact to the head and the object struck to identify those cases in which the provision of some means of energy absorption might reasonably be expected either to prevent or significantly reduce the severity of the injury to the brain in a similar crash. The results of this investigation indicate that there is considerable potential for reducing the severity and the consequences of impacts to the head by padding the upper interior of the passenger compartment. However, an even greater level of protection would be provided by the use of protective headwear.

Protective headwear, similar to a soft shell pedal cycle helmet, is estimated to be much more effective than padding the car in preventing cases of fatal brain injury and in improving the outcome in cases of severe brain injury. With each of these forms of protection the benefit appears likely to be greatest for cases which would otherwise sustain a brain injury of moderate severity (improved outcome in 40 and 25 per cent of cases respectively).

Headwear in the form of an energy absorbing head band covering the forehead and sides of the head would also provide a substantial level of protection (about half the benefits of a bicycle helmet).

In Chapter 4 the results of a Harm analysis are presented which estimate the likely financial community benefits which would be expected to come from the introduction of a range of countermeasures aimed at reducing head, neck and/or facial injuries to passenger car occupants involved in road crashes. "Harm" is a metric which estimates the societal cost of a given injury, taking into account the frequency with which that injury occurs as well as treatment, rehabilitation, loss of earnings, pain and suffering costs of injury. Obviously a Harm analysis needs to be based on a representative sample of crashes, as has been attempted in this report, if it is to yield nationally representative estimates.

The total annual benefit in terms of reduced Harm are estimated to be about $123 million for padding of the upper interior of the passenger compartment. The estimated benefit for protective headwear (in the form of a helmet) is between $380 million (assuming a fully airbag equipped fleet) and $500 million (assuming no vehicles with airbags). Estimated harm benefits are also given for other protective measures such as air bags alone, both front and side-mounted bags, and improved seat belt systems and penetration resistant side window glazing. The benefits are presented in terms of the savings per vehicle for two discount rates, 5 and 7 per cent. At the former discount rate the estimated benefit in savings of head and face Harm are $154 per car for padding of the upper interior, and $476 and $626 for protective headwear for cars with and without airbags.