Route 7 and Route 35: Two bridges, different jobs
A variety of complicating factors make the two state bridge reconstruction jobs in town quite different from each other, although they’re similar in size and — at $3.5 million for Route 7 and $3.2 million for Route 35 — fairly similar in cost.
The Route 35 bridge had room for construction of a temporary bridge, and as the most direct route to Danbury Hospital for town ambulances, officials didn’t want it to ever be totally shut down. That has been the fate of the Route 7 bridge, which closed twice in June, and will be again on three more planned weekend-long closures with traffic detoured through town.
Construction of a temporary bridge had to be done before work on Route 35 bridge could begin, extending the total work time.
And, night work isn’t permitted at that bridge, since it’s right beside the 287-unit Fox Hill condominium complex.
The Route 7 bridge doesn’t have room for a temporary bridge, necessitating the periodic closures. It is also a location where some night work is acceptable.
So, with “accelerated bridge construction” and periodic weekend-long road closures, the state’s Route 7 bridge re-construction is expected to be less time-consuming than the Route 35 bridge job, which has slowed travel on Route 35 for months now with periods of alternating one-way traffic.
The state’s goal is to have the both bridges reopened this fall — Route 35 by the end of November, and the Route 7 bridge sooner.
A major step in the Route 35 bridge project is expected to be the changeover from working on the southbound lane of the bridge, with both lanes of traffic rerouted slightly to the east, to working on the northbound lane while the new re-opened southbound lane handles southbound traffic — and northbound traffic continues to be rerouted on the temporary bridge on the eastern side.
Charles Murad, project engineer at the state’s Department of Transportation (DOT), described the the limitations of the Route 35 bridge project in a July 5 email.
“Our construction operations, per the contract, do not allow us to work at night except for utility work as not to disturb the Fox Hill Condo Residents,” he wrote.
“The utilities are presently being relocated for Stage I. Both the Eversource Gas main and Frontier communication duct banks have to be relocated in this stage. We are also installing drainage and completing the deck diaphragm pours. The contractor is striving to have Route 35 open by the end of November.
“The temporary bridge will be dismantled during the winter months.“
David Neelands, transportation engineer III with the DOT’s district 4 bureau of engineering and construction, also described the Route 7 project to The Press last week.
“...On Route 7, the replacement bridge is to be built in stages (phases) if you will. Each of those stages is a weekend detour closure,” he said.
“The logic from the designers was that there is very limited space around that bridge. The Norwalk river is on one side and Metro North railroad is on the other,” Neelands said. “It is very close to the Route 102 intersection, so alternating traffic with signals would be most disruptive causing even longer delays than is present with an average daily traffic (ADT) of 17,000 vehicles.”
Per Neelands, each stage is as follows:
- Stage 1 — install temporary sheet piling for the future abutments that will support the bridge;
- Stage 2 — install the piles to bedrock;
- Stage 3 — install the abutments in preparation of the new bridge;
- Stage 4 — the big weekend: remove the old bridge and abutments, shape and grade the river bank slopes and stabilize, install the new bridge deck and beams, install temporary concrete barrier curb, metal beam rail and temporary pavement; between stage 4 and 5 construct the new cast-in-place parapets and roadway wall;
- Stage 5 — remove temporary pavement, install concrete approach slabs, membrane waterproof bridge deck and install final pavement, metal beam rail, line strip, turf establishment.
“Doing a project in this manner is called ABC or ‘accelerated bridge construction’ — it’s not suitable everywhere but generally allows work to be done with minimal disruption,” the transportation engineer said.
“The difference between the two projects is Route 35 is a more traditional approach to construction,” he added. “There was room for a temporary bridge and that allowed two-way traffic and there are only two stages, one for each half of the bridge being constructed.”
Both projects suffered delays early on: the Route 35 bridge due to a sewer line which was found in a different location than expected and had to be relocated; the Route 7 job due to a “scour hole” that had to be dealt with after being discovered on the river bottom by the bridge.