Results
The majority of fatalities reported were among male drivers younger than 30 years. However, larger proportions of older adults were fatally injured compared with younger adults. And, although there appeared to be no differenc across gender for young drivers, a larger proportion of older male drivers were fatally injured compared with older female drivers.
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Alcohol use and fatal injuries |
The number of fatalities by age and BAC. The proportion of sober drivers fatally injured increased from 64.2% for drivers younger than 20 years to 88.5% for drivers aged 80 years and more. However, the relationship between BAC and fatality risk was ‘U'-shaped. Fatality risk initially decreased with increasing BAC, reaching the lowest point at a BAC of 0.05–0.09. It then increased with BAC to reach its maximum at a BAC of 0.30 or greater. Using the age category 40–49 years as an example, the ratio of fatally injured drivers to non-fatally injured drivers was 2.79 at a BAC of zero. At a BAC of 0.05–0.09, the ratio was 1.52. Yet, at a BAC of 0.30 or more, the ratio was 7.06. This pattern was consistent for the other age groups, although little data were available for older drivers.
Roughly 65% of all crashes where data were available involved front impacts, representing the largest source of fatalities. Right-side impacts were the next most frequent occurrence at 17.5%, followed by left-side (driver-side) impacts at 13.5%, and finally rear-end impacts in 3.5% of all cases. At best, one-third of drivers survived left-side impacts, irrespective of age. Rear-end and right-side impacts were fatal for smaller proportions of drivers. Whereas the proportion of fatalities following left-side and rear impacts was not dependent on age, it progressed with age for front and right-side impacts.
Approximately 84% of drivers with restraint data were not wearing a seatbelt at the time of the crash. Of the remaining 16%, most were wearing a three-point belt (shoulder and lap).The following analyses emphasize three-point belt use versus no belts.
The proportion of fatally injured drivers not wearing seatbelts ranged from a low of 47.8% for drivers younger than 20 years to a high of 59.1% for drivers aged 50–64. On the other hand, the proportion of fatally injured drivers wearing belts ranged from a low of 30.5% for drivers aged 40–49 years to a high of 44.6% for drivers aged 80 and over.
The difference between proportions of fatally injured drivers without belts and with three-point belts varied with age according to an inverted ‘U'-shaped curve. Thirty-five percent fewer drivers younger than 30 years died wearing belts compared with those not wearing belts. This proportion increased to 42% for drivers aged 30–39 and to 48% for drivers aged 40–49 years. From then onward, the belt advantage decreased to 40% for drivers aged 50–64, and 29 and 22% for drivers aged 65–74 and 80+ years, respectively.
Although air bag data were missing for 65% of the cases available, these data are not as supportive as seatbelt data. Air bags did not appear to have a protective effect on drivers younger than 40 years, appeared beneficial to drivers aged 40–64, but may have been detrimental to older drivers. Although these data also suggested an inverted ‘U'-shaped curve as found with seatbelts, the overall benefit of air bags without controlling for other variables such as the direction of impact is uncertain.
Data on vehicle deformity attested to the severity of the impacts. Vehicle deformity was ranked by investigating officers on a four-point scale; severe deformity was one extreme. Data were dichotomized as severe deformity or less severe. Approximately 94% of all vehicles were severely deformed following the crash. Consistently, proportionally more fatalities were found among drivers of severely deformed vehicles. Among drivers of severely deformed vehicles, smaller proportions of drivers younger than 30 years were fatally injured compared with other age groups.
The proportion of severely deformed vehicles also varied according to age. The ratio of severely deformed vehicles to less deformed vehicles decreased steadily with age. Specifically, among drivers younger than 20 years, the number of crashes resulting in severe deformity was 15.22 times that of crashes resulting in less severe deformity. This contrasts with a ratio of 10.57 for drivers aged 30–39, and 7.09 for those aged 80+.
Higher speeds were associated with more fatalities irrespective of age group. Overall, the youngest drivers fared better than other drivers, and the oldest fared worst. Whereas only 25% of drivers younger than 20 years were fatally injured in crashes at speeds of less than 56 kph (35 mph), 49% of drivers aged 80+ were fatally injured. The differential across age groups continued for other speed categories.
As shown with vehicle deformity, the proportion of crashes at different speed categories varied by age groups. For drivers younger than 30 years, the largest proportion of crashes occurred at speeds of 112 kph (70 mph) or more. However, for all other age categories the largest number of crashes occurred at speeds of 56–95 kph (35–59 mph).
Vehicle attributes examined included weight, wheelbase, model year, and age. Weight, wheelbase and model year were extracted directly from the FARS database. Vehicle age was obtained by subtracting the vehicle model year from the crash year. Descriptive statistics for these variables.
Given the practice of automakers to release new model year vehicles midway in the previous year, a number of vehicles had an age of -1. All vehicle variables were considered normally distributed with the exception of vehicle age, which was positively skewed. Vehicle age was transformed using the natural logarithm of vehicle age +2 (it is impossible to obtain a natural logarithm for a value of zero or less) and plotted. The distribution of the transformed variable approached normality. Multivariate models were tested with both the untransformed and transformed vehicle age data.
