You need to be at least 21 years old to get behind the wheel of a commercial motor vehicle in the United States, but fatal older truck driver accidents are drawing attention to the fact that there’s no set age for when you’ll have to turn in your keys. A recently released study suggests that the number of accidents involving older truck drivers—those over the age of 70—has increased in the past three years, suggesting that older truck driver accidents may be a growing cause of concern.

Investigative Report Links Big Rig Drivers Aged 70+ to Dangerous Driving Conditions

CBS News recently released a five-month long investigation into older truck driver accidents, finding not only an increase in older truck drivers on the road, but in accidents involving those drivers. According to their findings, in the last three years alone there has been a 19 percent increase in accidents involving commercial truck and bus drivers that range from their 70s to 90s.

In 2012 the National Highway Traffic Safety Administration found that 5.1 percent of all people injured in crashes involving large trucks were 66 years or older, and that 5.3 percent of all drivers of large trucks in fatal crashes were 66 years or older. Though the incidence of older truck driver accidents may sound low, there are still far fewer truck drivers over the age of 65 than under the age of 65 and the percentage offers cause for concern. Especially when factoring in another 2012 study that found solo semi truck drivers over 65 were most at risk of causing a semi truck collision.

Why Are Companies Hiring Senior Truckers?

The trucking industry is facing a staggering shortage: The American Trucking Associations estimated that the industry was in need of 48,000 drivers in 2015, and that same year, trucking industry analyst Noel Perry countered with a claim of 100,000. In their 2015 Talent Shortage Survey, ManpowerGroup identified drivers in their top 10 hardest jobs to fill at number five and made special note of truck drivers.

While demand for truck drivers is high overall, the over-65 crowd is particularly appealing to trucking recruiters, who are looking for people who may have retired from other jobs and/or have fewer family commitments to call them back home.

Meanwhile, truck driving remains in sharp contrast to certain job types, such as airline pilot, which have a mandatory retirement age based on the perceived physical and mental needs of the tasks involved. For truck drivers there is no mandatory retirement age, as long as they meet the older-age driving requirements for their state. Yet despite the National Highway Traffic Safety Administration issuing guidelines that recommend every state maintain older driver safety programs, there are still 17 states that do not have special requirements for older drivers.

Factors in Older Truck Driver Accidents

The link between older drivers and accidents is one that is hotly debated. Skeptics point to statistics that have found older drivers don’t crash as often, but those findings often don’t take into account the fact that older drivers tend to drive less than younger drivers. According to the Insurance Institute for Highway Safety, once you look at drivers per mile traveled, drivers over 70 have higher crash rates than middle-aged drivers.

For older truck drivers, time spent on the road is inevitably high—as high as their younger counterparts—but it doesn’t take a lot for them to pass tests that help them get behind the wheel, and those tests may not take into account the complications that come with age. Older drivers must pass a physical and meet the age-dictated requirements of their particular state, which may mean a vision test or a road test when their license is up for renewal. There’s a lot, however, those tests won’t catch.

Cognitive functioning often declines with age, and that can mean slower reaction times and dulled reflexes, both crucial skills for truck drivers. Hearing problems can deaden the sound of honking. Arthritic joints may not move as fast when faced with an oncoming accident. Not to mention that other health issues that can come with age are often paired with prescription medications that can further inhibit a driver’s ability.

These obstacles can be challenging enough for the average driver, but truck drivers may have their own health issues to complicate matters. In their 2014 National Survey of Long-Haul Truck Driver Health and Injury, the Federal Motor Carrier Safety Administration found that obesity is twice as high among long-haul truck drivers than in the national working population, and that the prevalence of self-reported diabetes among long-haul truck drivers is at 14 percent in comparison to the national working population, in which the prevalence sits at seven percent.

Combine those factors with age, and it’s no surprise older truck driver accidents are reportedly on the rise.