SHIRLEY — Though the estimated price tag for reconstructing Townsend Road is $3.7 million, Department of Public Works Director Joseph Lynch said the low bid, from P.J. Albert, of Fitchburg, came in at $3.1 million.

Six bids came back by the deadline date last month. The contract price figures in a 25 percent “big dig” contingency cost up front, said Lynch.

That’s the good news. The bad news is that if construction costs, paid with federal funds administered by the state, exceed the budget by more than 10 percent, the town pays the overrun.

“If it goes over 10 percent, we eat it,” said Lynch.

But the risk that will happen is low, he said. The contractor has worked in town before, the work is straightforward, and town representatives participate in management meetings as the process moves forward, he said.

“We do have some control,” said Lynch.

The selectmen must sign on for the state to execute the contract, he said. The board agreed to accept Lynch’s recommendation to use P.J. Albert.

“When do the detours start?” asked town administrator Kyle Keady. “People are asking.”

Preliminary work may start this fall, such as minor drainage and tree cutting, said Lynch, but no detours yet. Major work should begin next spring.