A woman who reeked of booze and tried to use a casino voucher to pay for a meal at a fast-food drive-thru window on Monday night now faces impaired driving and assault charges.

Police say they were tipped by an employee of the fast food restaurant, who grew suspicious of the woman's sobriety after she tried to pay for her meal with a casino voucher.

Officers soon spotted the woman swerving dangerously through traffic.

"EPS found the female driving erratically, speeding, driving on the centre line, and narrowly missing parked vehicles, " police said in a statement.

"Officers activated their emergency lights, but she kept driving."

Police say the driver was eventually pulled over in a parking lot a few minutes later, and was so disoriented she couldn't roll down her own window.

Officers opened the door to the driver's vehicle instead, and found an empty bottle of rum sitting in the front console.

Minutes after she was arrested on suspicion of impaired driving, the woman allegedly assaulted one of the police officers.

"Her speech was slurred; she was unable to stand up properly; and her breath smelled of alcohol," said the police statement, which thanked the restaurant staffer for calling the impaired driving tip line.

"We thank every person who has ever called to Curb the Danger. This program would not be successful without you. Your calls have, and continue to, save lives."