Fragility versus excessive crash involvement as determinants of high death rates per vehicle-mile of travel among older drivers

doi:10.1016/S0001-4575(01)00107-5

Accident Analysis & Prevention

Volume 35, Issue 2, March 2003, Pages 227-235

https://doi.org/10.1016/S0001-4575(01)00107-5 Get rights and content

Abstract

Using multiple national data systems, the roles of fragility (susceptibility to injury) versus excessive crash involvement in the increased fatality risk of older drivers per vehicle-mile of travel (VMT) were estimated. For each age and gender group, deaths per driver involved in a crash (a marker of fragility) and drivers involved in crashes per VMT (a marker of excessive crash involvement) were computed. Compared with drivers ages 30–59, those younger than 20 and those 75 or older both had much higher driver death rates per VMT. The highest death rates per mile driven, 13-fold increases, were observed among drivers age 80 or older, who also had the highest death rates per crash. Fragility began to increase at ages 60–64 and increased steadily with advancing age, accounting for about 60–95% of the excess death rates per VMT in older drivers, depending on age group and gender. Among older drivers, marked excesses in crash involvement did not begin until age 75, but explained no more than about 30–45% of the elevated risk in this group of drivers; excessive crashes explained less of the risk among drivers ages 60–74. In contrast, crash over-involvement was the major factor contributing to the high risk of death among drivers younger than 20, accounting for more than 95% of their elevated death rates per VMT. Although both fragility and crash over-involvement contributed to the excess death rates among older drivers per VMT, fragility appeared to be of over-riding importance. These findings suggest that measures to improve the protection of older vehicle occupants in crashes should be vigorously pursued.

Introduction

Personal mobility plays a pivotal role in normal daily living and social functions for people of all ages. In the United States, driving is the primary means of personal mobility, accounting for 92% of all daily person-miles of travel (FHWA, 1997a). For the elderly, the ability to drive a car is a significant predictor of quality of life, functional independence, and physical and mental health.

Because physiological functions, such as vision and reaction time, decline with increasing age and cognitive functions also may decrease, safety performance in older drivers has been a cause of public concern (Marottoli et al., 1994, Foley et al., 1995, McGwin et al., 2000, Lyman et al., 2001, Janke, 2001, Teed, 1996). The prevalence of dementia has been reported as about 30% among 85-year-olds (Skoog et al., 1993); however, the prevalence of dementia among drivers in their 80 s is unknown because many older people with dementia are likely to have stopped driving. Public concern also is related to the increasing percentage of the elderly in the United States population and the consequent increase in the number of older drivers, who are driving more than older people in earlier decades (FHWA, 1997b). In addition, age-related declines in physical health can increase the likelihood of poor outcomes among older vehicle occupants involved in crashes. Older people are at higher risk of fractures and chest injuries (Augenstein, 2001, Cavanaugh and Koh, 2001, Wang, 2001, Zhou et al., 1996, Hall and Owings, 2000) and are more prone to injuries related to seat belts (Augenstein, 2001, Cavanaugh and Koh, 2001, Zhou et al., 1996). Moreover, injuries among older occupants have a poorer prognosis (Barancik et al., 1986, Waller et al., 1986, Evans, 1988, Evans and Gerrish, 2001, Kim et al., 1995). Despite extensive research on aging and driving safety, it is unclear to what extent fragility and crash over-involvement separately contribute to the excess fatal crash rates among older drivers. Past research focused on either one or the other factor, but not their joint effects. The objective of this study was to examine age-related differences in the relative contributions of fragility and excessive crash involvement to fatal crash risk, while controlling for the quantity of exposure to vehicle travel.

The effects of gender in combination with age also were of interest because women have been described as having a greater risk of injury in crashes of equivalent severity (Evans and Gerrish, 2001). The role of fragility and crash over-involvement in relation to age was examined by vehicle impact point because of research reporting that older drivers have high involvement rates in side impact crashes (Cooper, 1990, Insurance Institute for Highway Safety, 2000, McGwin and Brown, 1999, Preusser et al., 1998, Zhang et al., 1998).

Section snippets

Methods

Older drivers (ages 60 or older) and young drivers (ages 16–19 and 20–29) were compared with drivers ages 30–59, the age group with the lowest death rate per mile driven.

Driver death rates per VMT

Driver death rates per unit of travel among both genders were much higher for the youngest and oldest age groups (Table 1). During 1993–1997, there were 11,801 driver deaths among 16–19-year-old, who drove about 420 billion miles during this period, and 10,318 driver deaths among those age 75 or older, who drove about 193 billion miles. For both male and female drivers, death rates per VMT were at their lowest during ages 30–59, started rising by ages 65–69, and then rose sharply after age 74.

Discussion

In this study, the decomposition method was used to explore the age variations in different outcome measures of driving safety. Fragility, as measured by risk of death when involved in a crash, appeared to be of over-riding importance in explaining the increased fatality risk per unit of travel among older drivers. Fragility started increasing at ages 60–64 and continued to rise with advancing age; its estimated relative contribution exceeded that of excessive crash involvement even among the

Acknowledgements

We would like to thank the following colleagues at the Insurance Institute for Highway Safety: Susan A. Ferguson for providing helpful comments on this paper and Robert Tabor and Kristi W. Lowe for providing editorial assistance. This research was supported primarily by the Insurance Institute for Highway Safety and in part by grants R01AG13642 and R01AA09963 from the National Institutes of Health and grant CCR302486 from the Centers for Disease Control and Prevention. The opinions, findings,

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Fragility versus excessive crash involvement as determinants of high death rates per vehicle-mile of travel among older drivers

Abstract

Introduction

Section snippets

Methods

Driver death rates per VMT

Discussion

Acknowledgements

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

J. Safety Res.

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

Accident Anal. Prev.

Public Health

Clinical visual perimetry underestimates peripheral field problems in older adults

Clin. Visual Sci.

Motor vehicle trauma in northeastern Ohio. Part I. Incidence and outcome by age, sex, and road-use category

Am. J. Epidemiol.

Older driver involvement in fatal and severe traffic crashes

J. Gerontol.

How safe were today’s older drivers when they were younger?

Am. J. Epidemiol.

Risks older drivers face themselves and threats they pose to other road users

Int. J. Epidemiol.

Female compared to male fatality risk from similar physical impacts

J. Trauma