Sports utility vehicles and older pedestrians

BMJ 2005; 331 doi: http://dx.doi.org/10.1136/bmj.331.7520.787 (Published 06 October 2005) Cite this as: BMJ 2005;331:787
  1. Ciaran Simms, lecturer in mechanical engineering (arhc{at}amnch.ie),
  2. Desmond O'Neill, associate professor of medical gerontology
  1. Trinity Centre for Bioengineering and Medical Gerontology, Trinity College Dublin, Ireland

    A damaging collision

    Two independent trends in the developed world are likely to reverse some of the hard won improvements that have been made in road safety. One is the ageing of the population; the other the increase in the use of sports utility vehicles (SUVs, high performance four wheel drive cars capable of off-road driving). The first trend produces a growing number of vulnerable road users; the second produces a likelihood of more severe injuries when vehicles and pedestrians collide. Public health professionals will need to work with transportation and road safety agencies to avoid the inevitable consequences of more vulnerable road users and more lethal vehicles.

    Among road users, pedestrians are already a group at high risk, and elderly pedestrians are particularly at risk. People over 60 are more than four times as likely to die if injured by a car than younger people1: in a pattern repeated around the developed world, older people in Ireland account for 30% of pedestrian deaths but only 11% of the population.2 The World Health Organization has recognised protection of older pedestrians as a key safety measure for this age group.3 Pedestrian protection is an even more pressing problem in the developing world. Pedestrian injuries and deaths from collisions with vehicles represent about 20% of automotive casualties in the European Union,4 but they rise to nearly 50% of casualties in developing countries, which have poorer roads and more travel by foot.w1

    Pedestrian protection is achieved in several ways. These include separation of vehicles from pedestrians, reduction of vehicle speeds,5 w2 w3the development of “smart vehicles” to avoid collisions, and improved vehicle design to reduce injuries to pedestrians.w4The proliferation of sport utility vehicles represents a backwards step in safer vehicle design.

    In Europe sales of SUVs have increased by 15% in the past year, while sales of standard cars have dropped by 4%.w5In Ireland, SUVs now represent almost 8% of new registrations. In the United States 40% of new vehicles purchased are classified as light trucks or vans (many of which are SUVs).6 Gabler and Lefler have used the US fatal accident reporting system database (FARS) to analyse the relative dangers posed to pedestrians by these high fronted vehicles. Their results show that, for the same collision speed, the likelihood of a pedestrian fatality is nearly doubled in the event of a collision with a large SUV compared with a passenger car.6 Other studies have consistently showing higher rates (up to four times greater) of severe injury and death for pedestrians in collisions with SUVs.79

    A common misconception is that the increased vehicle mass of SUVs is responsible for the increased hazard to pedestrians. In fact, although vehicle mass is important in car to car collisions, it is a minor factor in vehicle-pedestrian collisions given the disparity between the weights of the pedestrian and of the vehicle.w6The increased mortality and morbidity from SUVs arises primarily from the geometry of the front end structure. In a typical collision between a car and an adult, the bumper strikes the lower legs and the leading edge of the bonnet strikes the femur/pelvis, causing the pedestrian to rotate towards the bonnet. This results in the bonnet or windscreen hitting the shoulders or head. After this further injuries often occur through impact with the ground. A key mitigating factor in injury severity is the relatively peripheral nature of the primary impact of the bumper to the lower legs.w7-w9This affords some protection to the critical upper body regions in the primary impact, and the resulting body rotation on to the bonnet tends to further diminish the impact—a characteristic often called “wrap and carry.” The principal pedestrian injuries from cars are predominantly fractures of the tibia and fibula and knee injuries from the primary impact with the bumperw10and head injuries from the secondary impact with the bonnet or windscreen.w11

    SUV bonnets are higher than those of cars and this results in a more severe primary impact on the critical central body regions of the upper leg and pelvis.w12Also, there is less rotation as the impact is closer to the body centre of mass, resulting in a more efficient transfer of energy. For example, raising the bonnet leading edge height from 600 mm to 850 mm increases the impulse by a factor of about two.w13This results in a doubling of injuries to vulnerable regions such as the head, thorax, and abdomen.9

    Another group of vulnerable road users are small children, and a well described risk with SUVs are accidents in driveways, in which SUVs and light trucks are over-represented.w14 w15This is probably a result of the increased height of the SUV and the driver's reduced ability to see things around the vehicle.

    Thus the evidence shows that SUVs represent a significantly greater hazard to pedestrians than ordinary cars—and those pedestrians are getting older and more vulnerable. Addressing this threat requires an integrated approach from public health and transportation and road safety agencies (including vehicle designers). One measure should include changing crash investigation processes to identify SUVs in vehicle-pedestrian impact statistics. Given the increasing economic importance of the SUV market to car manufacturers, traffic safety activists in the health professions will need to keep pressure on governments to make sure they don't put economic and industrial interests ahead of effective safety strategies.10

    In the meantime, informing consumers of the increased risk to pedestrians from SUVs may represent a useful first step in raising public awareness. The Irish Medical Organisation has recently called on motor manufacturers and distributors to display warning notices on SUVs that advise potential purchasers of the increased risk of severe injury and death to pedestrians associated with these vehicles. Resistance from the industry to such initiatives is likely to be strong, just as it has been from the tobacco industry for warnings on cigarettes.11 Nevertheless, healthcare advocates should take heart from previous successful traffic safety initiatives.12 Addressing the hazards posed by SUVs to pedestrians is an emerging and real traffic safety challenge in the developed world.

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    • Competing interests None declared.