"Older drivers represent the fastest-growing segment of the driving population," the authors write as background information in the article. "As this segment of the population expands, so too have public safety concerns, given older drivers' increased rate of motor vehicle collision involvement per mile driven. Research has suggested that this increase may be partly attributed to medical, functional and cognitive impairments."

Little evidence links visual acuity to involvement in motor vehicle collisions. However, in January 2004, Florida implemented a law requiring all drivers 80 years and older to pass a vision test before renewing their driver's licenses. Gerald McGwin Jr., M.S., Ph.D., and colleagues at the University of Alabama at Birmingham used data from the National Highway Traffic Safety Administration and the U.S. Census Bureau to study rates of motor vehicle collision deaths among all drivers and older drivers in Florida between 2001 and 2006. They also compared these rates to those in Alabama and Georgia, neighboring states that did not change their legal requirements during this time period.

Overall death rates from motor vehicle collisions in Florida increased non-significantly between 2001 and 2006, but showed a linear decrease in drivers age 80 and older. When comparing the period before the law (2001 to 2003) to the period after the law (2004 to 2006), the fatality rate among all drivers increased by 6 percent (from 14.61 per 100,000 persons per year to 14.75 per 100,000) while fatality rates among older drivers decreased by 17 percent (from 16.03 per 100,000 persons per year to 10.76 per 100,000). Death rates among older drivers did not change in Alabama or Georgia during the same time period.

Several potential reasons exist for the decline in Florida, the authors note. "Perhaps the most apparent reason is that the screening law removed visually impairment drivers from the road," the authors write. "However, in reality, the situation is significantly more complex."

About 93 percent of individuals who sought a license renewal were able to obtain one, suggesting that only a small percentage of drivers were removed from the road for failing to meet the vision standards. Another possibility is that the vision screening requirement improved visual function overall, because many of those who do not pass the test on the first try seek vision care and then return with improved vision. Finally, those who believe they have poor vision may have been discouraged from renewing their license at all, voluntarily removing themselves from the road.

"Ultimately, whether the vision screening law is responsible for the observed reduction in fatality rates because of the identification of visually impaired drivers or via another, yet related, mechanism may be inconsequential from a public safety perspective," the authors write. "However, the importance of driving to the well-being of older adults suggests that isolating the true mechanism responsible for the decline is in fact important." Future research identifying this mechanism would allow states to implement laws that accurately target high-risk drivers while allowing low-risk older drivers to retain their mobility.

Note: If no author is given, the source is cited instead.

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