TOPSHAM -- The clock on what state transportation officials are calling the biggest road repair project in Maine in decades begins ticking at midnight Sunday.

That's when crews from Pike Industries Inc. will set up barricades, effectively shutting down 18 miles of southbound travel lanes on Interstate 295 between Gardiner and Topsham.

Pike Industries will then have until Aug. 30 to remove the top layer of concrete from the 36-year-old road, crush the bottom layer of concrete into a gravel like substance, before finally repaving the road with more than 180,000 tons of black top.

The project is expected to impact thousands of commuters who use the interstate as well as tourists visiting Maine at the height of the summer season.

"It's the Waldo-Hancock bridge of the road building world for us," said Jim Hanley, spokesman for Pike Industries, referring to the new Penobscot Narrows Bridge in Prospect that opened in December 2006.

The concrete road, which opened in 1972, has deteriorated badly over the years. Rather than keeping one southbound lane open during the repair -- a process that might have stretched the project over three years -- the state Department of Transportation decided that finishing the job faster would be better than slower, even if it meant closing the highway entirely.

"A project of this scope normally would have taken us three years," said Sterling Paul, the project's engineer.

"We're going to do it in 10 weeks. It's going to be 10 weeks of craziness."

Incentives have been built into the $28.5 million contract that could pay Pike Industries up to $2 million if it finishes before the Aug. 30 deadline. Late penalties could also be imposed if the paving is delayed by lengthy periods of rain.

The work begins at 12:01 a.m. Monday in Gardiner when crews will erect barricades. Once the southbound lanes and exits have been blocked off, crews will arrive around 5 a.m. to begin removal of the top three inches of concrete from the existing highway.

Materials will be trucked to and stored at a farm in Richmond.

By the middle of next week, another wave of construction crews will begin to crush the underlying concrete pavement. The road won't be paved until later.

Also on Monday morning a new U.S. Route 201 exit ramp will open to allow southbound motorists to avoid downtown Topsham by getting on I-295 near the Topsham Fair Mall, before heading south to Freeport or Portland.

U.S. Route 201 cuts through the towns of Topsham, Bowdoin, Bowdoinham and Richmond, and is one of two alternate travel routes recommended by the state.

Brad Foley, director of safety for the state transportation department, said the state plans to closely monitor U.S. Route 201 traffic, which is expected to increase from about 3,000 cars daily along that stretch to 13,000.

The MDOT has already installed signs, reflective road cones, a traffic light and mile markers with a mileage countdown to raise driver awareness, officials said.

The detour will add about 15 minutes to a commuter's trip, Foley estimated.

Bowdoinham Town Manager Kathy Durgin-Leighton said she has received so many inquiries about the project that she decided to post a reminder about the start date for the project on the town's Main Street message board.

Most of the town's residents commute to work outside Bowdoinham, she said.

"I would compare what we're going through to sitting on the edge of your seat. We're all just wondering what is going to happen," Durgin-Leighton said.

The other detour option for southbound motorists is the Maine Turnpike south from Augusta.

During construction, the Maine Turnpike Authority will offer free EZ passes to motorists impacted by the project, but the passes must be returned by October.

Commuter Larry Niles, who currently travels daily from his home in Falmouth to his job in Augusta at the Family Planning Association of Maine, said the closure will be inconvenient and more costly to him.

Niles will still travel north on the interstate but will be forced to take the turnpike at the end of his work day, a route he says will add about 10 minutes to his 45-minute commute.

"It's going to be a pain in the butt, but it will be a heck of a lot better than taking the detour," Niles said, referring to the faster speeds he can achieve on the turnpike.

Pat Eltman, director of the Maine Office of Tourism, said her office has worked closely with the state DOT to get the word out about the project to visitors.

"It needs to be done and there is not much we can do about it. Are we crazy about it? No. But it needs to be done," Eltman said.