At the Peterborough Select Board meeting Tuesday night, Tim Dunn of of the state Department of Transportation said reconstructing the bridge over the Contoocook River on Route 202 at the intersection of Route 136 presents complex challenges.

“The site is very constrained, and the alternatives for reconstructing the bridge are limited,” said Dunn, the project manager. “There is a whole lot going on right at that site.”

Constraints include the historic North Village dam, the intersection with Route 136 and Old Street Road, a public car-top boat launch, the Wilder thermometer factory historic site within Rotary Park and a town water line on the bridge.

The state-owned bridge has been on the red list since 2012 – meaning it gets inspected twice a year but is no unsafe, according to Dunn -- and is ranked No. 17 of bridges prioritized for reconstruction. Dunn noted that the bridge is a “scour-critical bridge,” meaning the force of water passing under the bridge removes streambed material from around the abutments and can lead to destabilization of the structure in the long term.

NHDOT has determined that the bridge must be completely reconstructed. Aaron LaChance of design firm Hoyle Tanner, who also worked on Peterborough’s Main Street Bridge project, said the three alternatives for replacement are an upstream shift, a downstream shift or replacement in the existing location. 

Lachance said the upstream shift would create minimal impact on existing structures, but that the downstream shift option would impact the intersection with Route 136 and the north end of Old Street Road as well as both utility lines.

“Impacting that intersection would be problematic, as it is already a tough intersection with a very steep hill,” Lachance said.

Replacing the bridge in the existing location would require multiple seasons of single-lane traffic on Route 202 during construction.

“We would be talking minutes rather than seconds of delay with that option,” Lachance said.

Both the upstream and downstream options include a temporary bridge, which would enable traffic to flow throughout  construction. 

“We are looking for feedback from the community, from all the shareholders, from everyone who will be affected by this project,” Lachance said.

The cost for the project is estimated at $10 million to $20 million. Dunn said the state would fund the replacement of the bridge, but the town would bear part of the cost of relocating sewer and water lines if necessary.

“Moving the sewer siphon would be a major financial consideration for the town. Having to adjust that is something we are really going to try to avoid,” Dunn said.

Select Board member Bill Taylor pointed out that the upstream shift seemed like the best option and asked if this was the favorite so far.

“They all have pros and cons and we have to balance everything   – cost, impact. It’s hard to know at this point which i  s better or worse, which of these alternatives meet the purpose and need for the project,” Dunn said. “That’s what we’ll be figuring out in  the next few months.”

Under the current schedule, NHDOT and Hoyle Tanner will finalize the alternatives analysis by November, complete preliminary plans by January and present the preferred alternative at a public meeting in spring 2024. A public hearing would take place in  summer 2024.

After final approval, expected in fall 2024, the final design  phase would take place in 2025-2026, with construction and project completion in 2027-2028.