Abstract
Crash rates per mile indicate a high risk of vehicle crash in older drivers. A reliance on mileage alone may underestimate the risk exposure of older drivers because they tend to avoid highways and travel more on nonfreeways (e.g., urban roads), which present greater hazards. We introduce risk-exposure density as an index of exposure that incorporates mileage, frequency of travel, and travel duration. Population-wide driver fatalities in the United States during 2002–2012 were assessed according to driver age range (in years: 16–20, 21–29, 30–39, 40–49, 50–59, 60–69, ≥70) and sex. Mileage, frequency, and duration of travel per person were used to assess risk exposure. Mileage-based fatal crash risk increased greatly among male (relative risk (RR) = 1.73; 95% CI: 1.62, 1.83) and female (RR = 2.08; 95% CI: 1.97, 2.19) drivers from ages 60–69 years to ages ≥70 years. Adjusting for their density of risk exposure, fatal crash risk increased only slightly from ages 60–69 years to ages ≥70 years among male (RR = 1.09; 95% CI: 1.03, 1.15) and female (RR = 1.22; 95% CI: 1.16, 1.29) drivers. While ubiquitous in epidemiologic research, mileage-based assessments can produce misleading accounts of driver risk. Risk-exposure density incorporates multiple components of travel and reduces bias caused by any single indicator of risk exposure.
Highlights
Crash rates per mile indicate a high risk of vehicle crash in older drivers
Annual travel frequency in trips per person increased gradually from ages 16–20 years to ages 40–49 years among male (relative risk (RR) = 1.11, 95% confidence interval (CI): 1.01, 1.23) and female (RR = 1.17, 95% CI: 1.06, 1.30) drivers (Figure 1A)
Age differences in driver risk have traditionally been assessed on the basis of crash rates per unit of travel (e.g., annual mileage [4,5,6])
Summary
Crash rates per mile indicate a high risk of vehicle crash in older drivers. A reliance on mileage alone may underestimate the risk exposure of older drivers because they tend to avoid highways and travel more on nonfreeways (e.g., urban roads), which present greater hazards. Crash rates are intended to control for differences in risk exposure for group comparison in crash risk This traditional method has led to reports of high crash risk among young and elderly drivers [5, 7,8,9,10], focusing road safety campaigns and legislation on the youngest and oldest drivers [10,11,12]. Among driver groups with medium to high annual mileage, the crash rate of older drivers was no greater than that of drivers in other age ranges. Langford et al [18] reported that crash rates were higher for all driver age ranges in the low-mileage group compared with medium- and Downloaded from https://academic.oup.com/aje/article-abstract/187/1/53/3865622 by Queen's University Belfast user on 04 September 2018
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