In an effort to combat drowsy driving, Uber announced today that it would require its most frequent drivers to take six-hour breaks after driving for 12 hours straight. Uber is updating the driver version of the app so that it logs off after counting 12 hours of driving, and drivers will not be able to log on until after the app registers six hours offline.

The update is expected to roll out nationally over a two-week period. Drivers will also receive a warning after 10 hours of driving to let them know they are approaching the 12-hour limit. A second warning will come after the 11th hour, and a third notification will serve as a 30-minute warning.

Uber is framing its new policy as an effort to combat drowsy driving. The company’s announcement includes statistics from the National Sleep Foundation and quotes from representatives of the Governors Highway Safety Association. Drowsy driving is the cause of up to 6,000 fatal crashes annually, according to the National Highway Traffic Safety Administration.

“We want to keep our riders and drivers safe,” said Sachin Kansal, Uber’s Director of Product Management, told The Washington Post. “The approach we have taken is irrespective of who’s responsible for managing this. We want to help the drivers manage that in the app so they have all the visibility, so they know how much they can drive and when they need to go offline.”

Kansal said the app will measure driving time using GPS and telematics to detect whether the vehicle is moving. Short waits, such as those at stoplights, will count against workers’ driving time. But longer waits such as those in airport cues, and other idling exceeding five minutes, will not count. Because the clock is cumulative, a driver can be prompted to take a break even if they haven’t driven driven for 12 hours consecutively. For example, someone who has picked up fares in two, six-hour spurts — without taking six hours of rest in between — would have their app disabled after the second leg.

Uber rolled out a similar policy in New York City in 2016, in which drivers who are on the road longer than 12 hours risked temporary deactivation. The policy followed a New York Post article that tracked a handful of Uber drivers who reported driving 16–19 hours a day. Meanwhile, Uber drivers in the UK are required to take six-hour breaks after 10-hour shifts in a new policy enacted earlier this year.