SAN FRANCISCO -- A California law granting driver's licenses to hundreds of thousands of people in the country illegally might have reduced the likelihood of hit-and-run collisions, according to a new study released Monday.
Researchers at Stanford University's Immigration Policy Lab estimated that granting driver-only licenses appears to have reduced hit-and-run crashes and saved insured drivers about $17 million that they would have absorbed from at-fault drivers fleeing collisions to avoid possible arrest.
Jens Hainmueller, faculty director of the policy lab, said the study was conducted because of a lack of data when California debated its law that went into effect on 2015.
"We thought we should provide some evidence," Hainmueller said.
However, Andrew Gelman, director of the Applied Statistics Center at Columbia University, said he would want more evidence to determine that the law decreased hit-and-run collisions.
"It would seem to me that lots of things can be driving the rate of collisions and the rate of hit and runs," said Gelman, who reviewed the study at the request of The Associated Press. "There are too many alternative explanations."
He agreed that the data does make it clear that granting the licenses did not decrease safety.
Supporters of the law have said people in the U.S. illegally would be less likely to leave the scene of an accident if they had a license and would not face the possibility of arrest.
The study of short-term effects found that issuing more than 600,000 driver-only licenses in 2015 had no discernable impact on the overall rate of traffic accidents.
Hainmueller said the report could aid other states considering similar policies.
"Our findings show that providing unauthorized immigrants with access to driver's licenses can create significant positive externalities for the communities in which they live," the report said in its conclusion.
Driver's licenses have long been a thorny topic in the U.S., where an estimated 11 million immigrants live without documentation, many in California. As of November, a dozen states offered such licenses, including Colorado, Delaware and New Mexico.
Proponents say legal driver's licenses boost public safety. Opponents say licenses grant a toehold to people who shouldn't be in the country.
Mark Krikorian, executive director of the Center for Immigration Studies, a Washington, D.C., think tank that supports tighter controls on immigration, dismissed the study as limited and premature.
"The point of giving driver's licenses to illegals is to document them, to give them partial amnesty," Krikorian said. "With these documents, they can more effectively embed themselves in society.
California has granted about 850,000 immigrant licenses under the law. The licenses are for driving only and the law prohibits safety officers from reporting drivers to federal immigration authorities.
There were more than 25.9 million licensed drivers in California in 2015.
The study found that the number of new driver's licenses issued in 2015 far outpaced the number of vehicles registered that year, suggesting that unlicensed immigrants had already been driving in registered vehicles.
The authors said follow-up studies are required to determine longer-term effects.
The study was published by the Proceedings of the National Academy of Sciences.