AUGUSTA — Work expected to start next week on a damaged bridge at exit 109A on the southbound side of Interstate 95 is expected to reroute drivers, and the change is expected to cause traffic delays.

Officials at the Maine Department of Transportation say something hit the ramp’s superstructure, damaging both the north and south exterior beams supporting the elevated roadway.

While the bridge has been deemed safe for all legal loads, department officials have determined the current bridge structure, built in 1959, should be replaced this winter by a new structure with a clearance that’s about a foot higher than the current 14-foot, 3-inch clearance. That’s expected to reduce the number of strikes that might damage the structure and to make its height consistent with the higher clearances of recently replaced bridges spanning the interstate.

“We advise travelers to seek alternate routes and plan ahead during peak commutes,” Ted Talbot, a department spokesman, said Thursday. The average daily traffic on that bridge ranges between 4,500 and 5,000 vehicles, he said.

While the project will inconvenience travelers, he said, the department plans to complete the project as safely, effectively and quickly as possible.

On Saturday, a crew is expected to pave and change road striping patterns, which may cause delays. Talbot said high wind is forecast for Saturday, and that may push back the start of the work.

Dale Doughty, director of maintenance and operations at the Department of Transportation, said the project, expected to cost $2.5 million to $3.5 million, will go out to bid this week. The contract is expected to be awarded next week and work should start by the week of Nov. 6, weather permitting.

Beginning on Monday, southbound drivers planning to travel east toward Augusta will be directed to use exit 109B and use the reverse-direction loops on Western Avenue to continue east toward downtown Augusta and the State House.

Doughty said that will give contractors time in November and December to build a new stretch of two-way roadway that will connect exit 109A with Whitten Road.

Once that’s done, he said, southbound traffic entering or leaving the interstate will be able to use exit 109A while the bridge is being replaced.

The damage to the south exterior beam was discovered Oct. 3 by a maintenance worker.

Bill Doukas, senior structural engineer in the DOT’s Bridge Maintenance Division, said a strike, probably by what the department calls a superload, resulted in a crack that stretches more than halfway across the bottom flange of the rolled steel I-beam and into the middle part of the beam.

Moving large objects on state roads requires permits. Routine permits are issued for loads that are a little heavier, wider or longer than normal loads.

Superloads are larger than that.

Doukas said the components of wind turbines are one kind of superload; transformers for electrical transmission systems are another.

“We also have heavy equipment, like excavators or logging equipment, things with arms that are up on trailers that are pulled on the back of trucks,” he said, adding that they might strike overpasses.

No one knows what struck the bridge. The department has been investigating the cause of the damage with little success. Anyone with information about the damage is asked to call the DOT’s legal division at 624-3020.

“Normally, bridges are inspected every 24 months,” Doukas said. “If they’re fracture-critical, they’re inspected every 12 months.”

In this case, he said, the worker was looking over the bridge, as maintenance workers are encouraged to do, and discovered the crack.

To shift the weight of traffic off that part of the bridge, he said, the department put out barrels along south edge of the road.

The damage to the north side of the bridge appears to align with the damage on the south edge, Doukas said, so it was probably the same incident. The middle three beams were not damaged because they set are higher to accommodate the pitch of the roadway.

The department also is expected to install an over-height load warning system to protect other bridges spanning the interstate, including the Western Avenue overpass.

Jessica Lowell — 621-5632

jlowell@centralmaine.com

Twitter: @JLowellKJ