Colorado’s winter driving restrictions on a mountain stretch of Interstate 70 will be in full force for nine months beginning Sept. 1 under a bill signed into law Friday by Gov. Jared Polis.

The beefed-up traction law takes particular aim at drivers of two-wheel-drive passenger vehicles. Each September through May, they will face the requirement of having specialized winter tires or carrying traction devices while traveling on I-70 between Dotsero and Morrison. The old traction law had been activated only before and during actual winter weather.

House Bill 1207 also increases the minimum tread depth for tires on all vehicles — including those with four-wheel-drive — from an eighth of an inch to three-sixteenths of an inch.

Though I-70 is the only highway corridor where the increased restrictions will be in effect for nine months a year, they will apply to other corridors when the state activates the traction law for storms.

“While the views can be breathtaking, the conditions can be downright frightening during the winter,” Polis said in remarks prepared for the afternoon bill-signing ceremony near the Eisenhower-Johnson Memorial Tunnel. “We know how dangerous they can be without having chains, tread depth or four-wheel drive. This bill will help keep drivers safer on the road.”

In approving the revisions, the legislature directed the Colorado Department of Transportation and the Colorado State Patrol to explore ways to step up enforcement of the traction law.

Drivers of vehicles without four-wheel-drive or all-wheel-drive can comply with the traction law by having either snow tires (with or without studs) or by using all-season tires with a mud/snow designation (often marked on the sidewall with “M+S”). But experts say the latter type are less effective on ice and in slush.

Owners of two-wheel-drive vehicles with standard tires can carry chains or an AutoSock set in the trunk to use when winter weather strikes.