Requirements for the crash protection of older vehicle passengers
This study compares injury outcomes in vehicle crashes involving different age groups of belted passengers. Two datasets were considered. Firstly, UK national data revealed that younger passengers are much more likely to be involved in crashes per million miles travelled compared to older passengers although older passengers are much more likely to be killed or seriously injured compared to younger passengers. Secondly, in-depth vehicle crash injury data were examined to determine some of the underlying reasons for the enhanced injury risk amongst older passengers. In crashes of approximately equal severity, the older passenger group were significantly more likely to be fatally injured in frontal crashes (p<0.001). However young passengers were as equally likely to be killed in struck-side crashes compared to the older group. The results also showed that older passengers sustained more serious injuries to the chest region in frontal crashes compared with the younger aged group (p<0.0001) and it is this body region that is particularly problematic. When the data were analysed further, it was found that a large proportion of passengers were female and that in the majority of cases, the seat belt was responsible for injury. Since by the year 2030, 1 in 4 persons will be aged over 65 in most OECD countries, the results suggest a need for intervention through vehicle design including in-vehicle crashworthiness systems that take into account reduced tolerance to impact with ageing. It is generally acknowledged that the energy required to cause an injury reduces as a person ages (Augenstein, 2001). It therefore follows that older vehicle occupants are more vulnerable to injury in a crash compared with their younger counterparts. The skeletal structures of older persons are more easily damaged and the consequences of any assault are likely to be more serious compared with younger vehicle occupants because of reductions in bone strength and fracture tolerance (Dejammes and Ramet, 1996; Evans, 1991; Mackay, 1989; Viano et al, 1989). The high prevalence of osteoporosis particularly amongst females is well established (Berthel, 1980). Nevertheless, although manufacturers have an increased awareness of the physiological changes that take place in later life, the evidence upon which effective crash protection design is based is sparse, particularly regarding the needs of older occupants (Mackay, 1989). In one study, Foret-Bruno, (1978, 1989, in Dejammes and Ramet, 1996) concluded that older people could withstand a chest load of 5,000 Newtons (equating to 50mm of force-deflection on a Hybrid-III anthropomorphic crash-test dummy) whilst young people could withstand a chest load of 8,000 Newtons (equating to 80mm of force-deflection). The implication of this is that an older car occupant is several times more likely to sustain a life-threatening chest injury (Padmanaban, 2001). The chest is clearly a vulnerable area and the major load bearing area for restraint systems as well as a major point of contact with the vehicle structure in a crash. However, the level of personal mobility and independence afforded by the motorcar is valued highly by older people. Many older people in western countries now make an overwhelming proportion of their trips in private vehicles (OECD, 2001) compared with 30 years ago or so. With this in mind, there is a growing awareness of the need for vehicle safety to suit older occupants. In short, there is a need to improve the crashworthiness of vehicles to provide better protection for older occupants in the event of a crash. Although there is much data concerning driver performance degradation with ageing, the effect of ageing on injury outcomes in vehicle crashes is still largely unclear. Evans, (1991) noted that age effects are largely difficult to determine. This study follows on from previous work examining ‘Older Occupant’ outcomes in vehicle crashes. A previous study examined injury outcomes for ‘Older Drivers’ (Morris et al, 2002). Such studies are deemed necessary in view of the growing recognition of the increase in the numbers of elderly persons in most westernised societies. Moreover, as noted by Mackay and Hassan, (2000) more detailed crash data are needed to optimise vehicle crash performance. The aims of the study were deemed as follows; • To examine crash and injury characteristics that may affect older passenger outcomes in the event of a crash; • To make some preliminary assessment of the need for countermeasure development.