Drivers must vacate the left lane when a vehicle comes up behind them, unless they are passing another vehicle, avoiding debris on the road, allowing traffic to merge from the right, preparing to turn left or passing an official vehicle stopped on the highway.

That will be the rule any time when the speed limit is 80 km/h or higher and traffic is moving at more than 50 km/h, under changes coming to the Motor Vehicle Act.

Hogging the left lane and holding up traffic is already a ticket offence, but one that police found difficult to enforce due to the wording of the legislation, said Transportation Minister Todd Stone. The fine continues to be $109 for inappropriate use of the left lane.

Stone said slow drivers in the left lane are a big frustration, prompting drivers to pass on the right, which is also illegal. The changes are not intended to encourage people to exceed the speed limit in the left lane, he said.

Amendments tabled in the B.C. legislature Monday also aim to clarify the province's roadside driving prohibition law, after court challenges. That law gives police powers to impound vehicles and suspend driving privileges for up to 90 days after a driver blows a "warn" level of blood alcohol on a roadside screening device.

The "immediate roadside prohibition" program took effect in 2010, effectively replacing most impaired driving charges with administrative penalties, including a three-day driving ban and a $200 administrative fee for those who register between 0.05 and 0.08, if the police officer has reason to believe the driver is impaired.