A mandatory cognitive screening policy targeting older drivers appeared to lower car crashes involving people over 70, according to results from a large population-based study using data from Japan.

But the same study, published in the Journal of the American Geriatrics Society, also reported a concurrent increase in pedestrian and cycling injuries, possibly because more older former drivers were getting around by alternative means. That finding echoed a 2012 study from Denmark, which also looked at the effects of an age-based cognitive screening policy for older drivers, and saw more fatal road injuries among older people who were not driving.

While some governments, including those of Denmark, Taiwan, and Japan, have implemented age-based cognitive screening for older drivers, there has been little evidence to date that such policies improve road safety. Guidelines issued in 2010 by the American Academy of Neurology discourage age-based screening, advising instead that people diagnosed with cognitive disorders be carefully evaluated for driving fitness and recommending one widely used scale, the Clinical Dementia Rating, as useful in identifying potentially unsafe drivers.

Japan’s national screening policy: Did it work?

The new study, led by Haruhiko Inada, MD, PhD, an epidemiologist at Johns Hopkins University in Baltimore, used national crash data from Japan, where since 2017 all drivers 75 and older not only must take cognitive tests measuring temporal orientation and memory at license renewal, but are also referred for medical evaluation if they fail them. People receiving a subsequent dementia diagnosis can have their licenses suspended or revoked.

Dr Haruhiko Inada

Dr. Inada and his colleagues looked at national data from nearly 603,000 police-reported vehicle collisions and nearly 197,000 pedestrian or cyclist road injuries between March 2012 and December 2019, all involving people aged 70 and older. To assess the screening policy’s impact, the researchers calculated estimated monthly collision or injury incidence rates per 100,000 person-years. This way, they could “control for secular trends that were unaffected by the policy, such as the decreasing incidence of motor vehicle collisions year by year,” the researchers explained.

After the screening was implemented, cumulative estimated collisions among drivers 75 or older decreased by 3,670 (95% confidence interval, 5,125-2,104), while reported pedestrian or cyclist injuries increased by an estimated 959 (95% CI, 24-1,834). Dr. Inada and colleagues found that crashes declined among men but not women, noting also that more older men than women are licensed to drive in Japan. Pedestrian and cyclist injuries were highest among men aged 80-84, and women aged 80 and older.

“Cognitively screening older drivers at license renewal and promoting voluntary surrender of licenses may prevent motor vehicle collisions,” Dr. Inada and his colleagues concluded. “However, they are associated with an increase in road injuries for older pedestrians and cyclists. Future studies should examine the effectiveness of mitigation measures, such as alternative, safe transportation, and accommodations for pedestrians and cyclists.”

No definitive answers

Two investigators who have studied cognitive screening related to road safety were contacted for commentary on the study findings.

Dr Anu Siren

Anu Siren, PhD, professor of gerontology at Tampere (Finland) University, who in 2012 reported higher injuries after implementation of older-driver cognitive screening in Denmark, commented that the new study, while benefiting from a much larger data set than earlier studies, still “fails to show that decrease in collisions is because ‘unfit’ drivers were removed from the road. But it does confirm previous findings about how strict screening policies make people shift from cars to unprotected modes of transportation,” which are riskier.

In studies measuring driving safety, the usual definition of risk is incidents per exposure, Dr. Siren noted. In Dr. Inada and colleagues’ study, “the incident measure, or numerator, is the number of collisions. The exposure measure or denominator is population. Because the study uses population and not driver licenses (or distance traveled) as an exposure measure, the observed decrease in collisions does not say much about how the collision risk develops after the implementation of screening.”

Older driver screening “is likely to cause some older persons to cease from driving and probably continue to travel as unprotected road users,” Dr. Siren continued. “Similar to what we found [in 2012], the injury rates for pedestrians and cyclists went up after the introduction of screening, which suggests that screening indirectly causes increasing number of injuries among older unprotected road users.”

Dr Matthew Rizzo

Matthew Rizzo, MD, professor and chair of the department of neurological sciences at the University of Nebraska Medical Center and codirector of the Nebraska Neuroscience Alliance in Omaha, Neb., and the lead author of the 2010 AAN guidelines on cognitive impairment and driving risk, cautioned against ageism in designing policies meant to protect motorists.

“We find some erratic/weak effects of age here and there, but the big effects we consistently find are from cognitive and visual decline – which is somewhat correlated with age, but with huge variance,” Dr. Rizzo said. “It is hard to say what an optimal age threshold for risk would be, and if 75 is it.”

U.S. crash data from the last decade points to drivers 80 and older as significantly more accident-prone than those in their 70s, or even late 70s, Dr. Rizzo noted. Moreover, “willingness to get on the road, number of miles driven, type of road (urban, rural, highway, commercial, residential), type of vehicle driven, traffic, and environment (day, night, weather), et cetera, are all factors to consider in driving risk and restriction,” he said.

Dr. Rizzo added that the 2010 AAN guidelines might need to be revisited in light of newer vehicle safety systems and automation.

Dr. Inada and colleagues’ study was funded by Japanese government grants, and Dr. Inada and his coauthors reported no financial conflicts of interest. Dr. Siren and Dr. Rizzo reported no financial conflicts of interest.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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