States that let unauthorized immigrants get driver’s licenses make their roads safer for all, a new study suggests.

After implementing one such law in January 2015, California saw a 7- to 10-percent statewide drop in hit-and-run accidents that year, Stanford researchers report Monday in PNAS. That equates to roughly 4,000 fewer hit-and-runs for the year. In that time frame, more than 600,000 unauthorized immigrants got licenses, and the numbers of accidents and traffic fatalities were unchanged by the law.

“Overall, the findings suggest that providing driver’s licenses to unauthorized immigrants led to improved traffic safety,” the authors conclude.

The findings offer some long-needed data to the debate on such policies. Currently, 12 states and Washington, DC have adopted laws allowing people living in the country without legal permission to obtain licenses to drive. California’s law, dubbed AB60, allows unauthorized immigrants residing in California to drive legally. And it explicitly prohibits law enforcement officers from reporting license holders to immigration officials.

Critics contend that licensing unauthorized immigrants will lead to more accidents and less safe roadways. They reason that such motorists: will likely end up driving old, poorly maintained cars; are unlikely to buy insurance; may not be able to decipher English road signs; and may hail from places where fleeing the scene of an accident is acceptable.

Proponents argue that training, testing, and licensing unauthorized immigrant drivers—who are likely to be driving with or without a license—can only improve traffic safety. Plus, licensing drivers can dash their fears of deportation or other legal consequences for driving or getting in an accident. This might make it more likely that those drivers will seek insurance coverage and stick around at the scene of collisions.

Road to data

This last part is critical for overall traffic safety, the authors of the new study explain. Having drivers stay at the scene doesn’t just make sure that the at-fault driver pays up—it helps ensure that authorities are notified quickly. When this happens, police can secure the area to prevent victims from being hit again or other accidents from happening. It also means injured people won’t suffer any delays in medical treatment, which could increase the severity of injuries or even lead to death.

To sort out the issue, the researchers sifted through California state traffic accident records and Department of Motor Vehicle licensing and registration records. They found that licensing of unauthorized immigrants varied widely by county after AB60 was enacted.

This county-by-county variation was helpful in sorting out what statewide trends could be linked to the new licenses. For instance, the researchers found a decline in accidents per capita following the adoption of the law. But that trend was unrelated to licensing, i.e., counties with the biggest shares of newly licensed unauthorized immigrant drivers didn’t necessarily see the biggest reductions in traffic accidents.

The researchers did find a link between the new licenses and fewer hit-and-runs, however. They also noted that there wasn’t a boom in vehicle registrations, despite the state issuing more than 600,000 new licenses in 2015 under the law. This suggests that unauthorized immigrants were likely on the road prior to having a license.

The study simply provides a correlation; it doesn't say for certain whether AB60 caused fewer hit-and-runs. However, the authors say the findings drive home the idea that unauthorized immigrant drivers, licensed and protected from deportation, are more likely to stay at the scene of an accident. This not only boosts safety, but could also lower insurance costs driven up by hit-and-runs, the authors argue.

PNAS, 2017. DOI: 10.1073/pnas.1618991114 (About DOIs).