The Bath Viaduct reopened Wednesday, nearly a month ahead of schedule.

Traffic had been detoured through downtown Bath since October, as contractors for the Maine Department of Transportation demolished and rebuilt the highway span. The $12 million project had been scheduled to finish Memorial Day, but was completed ahead of schedule, DOT officials said.

“It’s been a truly successful project,” said Glenn Philbrook, the MDOT resident engineer for the project. “It’s a great day.”

The original viaduct, built in 1958, was in dire need of replacement. Exposed rebar, deteriorating concrete and a high-profile accident in which an SUV went off the overpass were all signs that the project was needed.

The viaduct carries Route 1 over Bath. Approximately 18,000 vehicles a day travel the highway.

“There was a lot of concrete deterioration,” said Wayne Frankhauser, program manager of MDOT’s bridge program. “It was at the point it needed to be replaced.”

During the construction, work crews replaced 19 concrete piers with 20 spans, 1,900 linear feet of roadway, 240 feet of railing lines, 1,200 feet of sidewalks, and more than 1,800 feet of sewer pipes, while rerouting thousands of cars that pass through every day.

“The lane closure matrix that was built into the contract was incredibly complicated,” said Philbrook. He cited dealing with traffic as the most difficult portion of the project.

Completing the project quickly was important, said Frankhauser. “I think it’s well known that Route 1 is an important link to everyone Down East in Maine,” he said.

Nearby residents and businesses said they appreciated the work MDOT and contractor Reed & Reed did to complete the project with few disturbances.

“Although we did have to give our customers and delivery drivers some extra help finding us during construction, it wasn’t at all as bad as we were warned it might be,” said Gretchen Jaegar, owner of Halcyon Yarn. Halcyon, located on the corner of Washington Street and Route 1, is just a few dozen feet away from the viaduct and had a front-row view of the work all winter.

“The crew working on the construction did a great job and were very responsive when we had concerns,” said Jaegar. “Overall we’re really pleased that it’s opening ahead of schedule and eager for the area to be much improved by the time it’s all done.”

The traffic relief is a plus, but for Jerry Larochelle, owner of The Sandwich Shop, having the road beneath the viaduct open to pedestrian traffic is the biggest advantage.

“It’s been a hard winter,” said Larochelle.

The Sandwich Shop is located across Route 1 from Bath Iron Works. Before the viaduct work began, employees would regularly walk across the street for lunch, but since October, pedestrian passage under the viaduct was difficult, cutting into Larochelle’s business.

“Hopefully, they’ll finish it up real fast,” said Larochelle.

The work underneath the viaduct, which Philbrook calls the “Bath beautification” portion of the project and includes new plantings, some cobblestone surfaces and repair work on the roads damaged during the project, will take a few more months.

That work is scheduled to be completed sometime this summer. For more information on the viaduct project, visit maine.gov/mdot.