Laconia-Gilford Bypass bridge rehab project to begin next summer, last 9 months

LACONIA — A city bridge will be replaced next summer on the Laconia-Gilford Bypass as part of New Hampshire’s 10-year transportation plan, and engineering studies have begun. 

At the Monday city council meeting, staff of the New Hampshire Department of Transportation, along with McFarland Johnson, an engineering and design firm based out of Concord, gave a presentation on the upcoming project, as well as its timeline. The work focuses on a bridge on U.S. Route 3 and NH Route 11, over Mile Hill Road. 

All told, the project will take about nine months. 

Bridge conditions mean NHDOT staff need to complete a rehabilitation project instead of a replacement — for more than one reason. Currently, the bridge is rated condition 5, nearing addition to the state’s red list of locally-owned bridges. The scale is 0-9, with 9 being the best, or “brand new”, and 0 being “on the ground.” The rating of 5 means there's work to be done.

While the bridge is perfectly safe and usable, some of the bridge components in need of TLC include cracks and water intrusion on the deck, and cracks in some beams and diaphragms. Additionally, the railing on the bridge deck is too short, and fails to meet state code requirements.

It’s also too soon to replace the whole bridge, which was built in 1967, said Sam White, project manager with McFarland Johnson.  

“The full bridge replacement was looked at mostly as a benchline, but from a cost perspective, looking at a life cycle, it’s just not the time for a full bridge replacement,” he said. “We still got good life on the substructures that are there with the rehabs we'd be doing on it, so that cost just isn’t justified, ultimately.”

In addition to a full bridge replacement alternative, two rehabilitation approaches were reviewed. 

Alternative 1 focuses on a deck replacement, which would rehabilitate concrete beams, diaphragms and abutments. The bearings, along with the abutment backwalls and deck joints, will be replaced in this scenario. 

Alternative 2 is a complete superstructure replacement that includes girders, the concrete deck and new pavement. The bearings, abutment backwalls, bridge railing and deck joints would all be replaced. Finally, the concrete abutments would be rehabbed. The second option was ultimately recommended as the construction path forward. 

“Alternative 2, which is the recommended alternative, is a full superstructure replacement. This addresses a few other concerns with the deck replacement. There are some concerns about having to load-post the bridge based off of just the structural components that are part of the beams today that we can’t address,” White said. “We would address the condition, but bringing it up to added strength is costly. This alternative removes the existing beams, replaces it with new structural steel and removes that issue altogether.”  

Traffic will be impacted throughout the duration of construction with one-lane, alternating two-way traffic. The other alternative — two-way traffic — wasn’t feasible, given the lane width, although much consideration was given, considering 8,900 people travel the bridge by car a day. 

Traffic isn’t suspected to be an issue, though. 

“We were held to that one-way, alternating two-way traffic signal-controlled scenario,” White said.  

Studies were done regarding environmental resources, and there are no impacts to wetlands, and no environmental permits are needed. Additionally, the project has no effect on historic resources in the area. 

“This is more of a footprint project. Really, we’re staying in the footprint of the road. We did review the area for natural resources and rare species; did not find any that would be impacted by the project,” White said.  

The preliminary project design is slated to be completed this month, and the next major deadline is in September, when the final design will be done. NHDOT staff will advertise the job beginning in October, and construction will begin in summer of 2027. 

Funding for the project comes from federal and state resources, and Laconia is not required to match any monies.

For more information, visit laconianh.gov.

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Katlyn Proctor can be reached at katlyn@laconiadailysun.com or by calling 603-524-0150.