DECATUR, Alabama - Traffic humming along Interstate 65 is about to slow down.

Drivers planning to use I-65 for the next three weeks may want to find another route to avoid the Tennessee River bridges.

A contractor will begin a maintenance project on the bridges Monday morning that will have one lane in each direction closed on the major artery that stretches from Chicago to Mobile. Traffic could back up for several miles at peak travel times.

Alabama Department of Transportation officials are urging local residents to find alternative routes while the work is underway to alleviate traffic congestion.

The DOT two years ago ran a computer model to determine how far traffic would back up if one lane was closed on either bridge.

The worst case scenario was a backup of about 12 miles -- reaching to about where the Tanner exit is -- of cars and trucks southbound on a Saturday afternoon in July, Allen Teague, pre-construction administrator for the DOT's 1st Division, said at media briefing this afternoon about the project.

That image should be enough to convince local travelers to avoid the bridges while they're down to one lane.

"They would only do it once or twice," Teague said.

The DOT is doing a media blitz of ads and news stories through newspapers, television and radio to warn motorists of the upcoming work. The DOT is also placing flyers and posters in rest stops and in businesses at I-65 exits all the way into Tennessee, DOT spokeswoman Rebecca Leigh White said at the briefing at the DOT district office outside Decatur. The Tennessee Department of Transportation is also helping warn I-65 motorists about possible delays and suggested alternative routes.

Electronic message boards will be placed along I-65 informing motorists of alternative exits.

"We want to make this as smooth as possible for travelers," White said.

Suggested northbound alternative exits are at Lacon, Thompson Road and Alabama 36 in Hartselle, and Alabama 67 in Priceville. Southbound alternative exits are at U.S. 31 north of Athens and at Tanner.

Officials are asking southbound motorists not to use the Alabama 20/Interstate 565 exit as an alternative "because it's already heavily traveled and we don't want to further impede traffic," Teague said.

Interstate Improvement Inc., a Minnesota company awarded a $6.8 million contract for the repair job, planned to start setting out construction signs Thursday or today in preparation for starting work on the bridges at 7 a.m. Monday.

Once the company starts work Monday, it doesn't plan to stop until the job is done. That means it will work around the clock every day of the week.

The DOT contract gives the company 20 working days to complete the project.

"They feel they can complete the project in less than 20 days," Teague said.

The contract does not include an incentive reward for Interstate Improvement to complete the project early, but there is a standard $3,100 a day penalty for each day the company misses the deadline, White said.

The maintenance project involves repairing the bridge decks where the concrete has chipped away and applying a protective, non-skid surface on the bridge deck.

Teague said the work is needed to extend the life of the bridges that opened in 1973.

The work zone speed limit will be 50 mph. Two state troopers are expected to be on the site when work starts Monday morning.