Nor(walk) River Railroad Bridge: Replacement Design Alternatives Explored in the Environmental Assessment/ Environmental Impact Evaluation (EA/EIE)
The Connecticut Department of Transportation (CTDOT) evaluated more than 70 replacement design variations prior to selecting the 240' Vertical Lift Span Bridge. The alternatives assessed fell within the following categories:
Representative options in each category were evaluated against factors such as local impacts, construction duration, impacts to rail service, and cohesion with the project's purpose & need.
While each alternative has varying impacts, there is no viable alternative that results in a markedly shorter construction timeframe or significantly fewer construction impacts than the 240' Vertical Lift Span Bridge preferred alternative. The figures for the alternatives outlined below are based on the concepts prepared for the Environmental Assessment and Environmental Impact Study published in 2016.
A "no-build" alternative is not viable due to the systemic nature of the 124-year-old bridge's deteriorated condition. The existing bridge, while safe for travel, suffers from extensive section loss due to corrosion, widespread fatigue damage, excessive mechanical wear, and obsolete electrical systems leading to higher maintenance costs.
Extending the Walk Bridge's life span by 100 years through rehabilitation requires the strengthening or replacement of thousands of internal and external components. Systems requiring attention include steel trusses, bridge piers, foundations, abutments and retaining walls; mechanical, electrical and architectural components; track and catenary systems; and the high tower transmission structures. Despite the extensive breadth of work required to strengthen and repair the bridge's deficiencies, the underlying structure would still be more than 120 years old.
Rehabilitation work is performed directly adjacent to the operating railroad. This proximity to the active rail line results in restrictive limits on construction, extending the project's duration and inflating costs. A rehabilitation option would require the construction of a temporary two track bridge to the north of the existing bridge. This temporary structure would limit marine traffic to only those vessels that don't require an opening.
The Walk Bridge Program evaluated two fixed bridge alternatives in the EA/EIE: a low-level fixed bridge and a modified low-level fixed bridge.
It's important to note that a fixed bridge alternative has no movable component, limiting the vertical clearance and maritime access on the waterway. The Norwalk River has active waterway users utilizing the river upstream. The United States Coast Guard (USCG) advised the project that a 60' vertical clearance, matching that of the upstream Yankee Doodle Bridge (I-95), would meet the reasonable needs of navigation on the river.
The low-level fixed bridge alternative retains the existing height and grade of the railroad tracks over the Norwalk River, while imposing a fixed limit on the vertical clearance between the bridge and waterway. This alternative requires multiple piers to be constructed in the water, resulting in a larger environmental footprint than other alternatives.
The low-level fixed bridge design fails to meet the reasonable needs of navigation as outlined by the USCG. Based on continued consultation with the USCG, if a low-level fixed-bridge was suitable, the USCG would have indicated as such during on-going consultations with the Program.
This modified low-level design envisions a fixed bridge constructed on the same horizontal alignment as the preferred movable alternative, with a vertical clearance of 26' and a channel width of 170'. Unlike the previous low-level alternative, this design removes the need for multiple foundations in the water. New foundations would be constructed at similar locations as the movable option, creating the same construction efficiencies as the movable alternative and promoting safer vessel movements with improved channel alignment.
The modified low-level fixed bridge would be a through truss, like the vertical lift alternative. The elimination of movable bridge elements such as lift span towers, mechanical equipment, electrical equipment and utilities result in an approximately 15% cost savings. However, this alternative is costlier than the original low-level fixed bridge that was evaluated, due to the larger quantities of steel and concrete necessary to accommodate a longer span.
This option would restrict navigability on the Norwalk River for all vessels taller than 26', and would prevent future dredging of the Norwalk River north of the Bridge.
A movable bridge is a structure that moves to provide passage for waterway vessels.
Three different movable bridge designs were advanced through the EA/EIE:
A rolling bascule style bridge uses a counterweight to continuously balance the bridge span as it's lifted to make way for maritime traffic. This bridge design shares commonalities with the Stroffolino roadway bridge in Norwalk, except that this design has only one span (or leaf) that "rolls open," whereas the Stroffolino bridge has two leaves.
This bridge design was not advanced because it proved to have the longest construction duration of the movable options, and the greatest impact to continuous two-track rail service on the New Haven Line.
A vertical lift bridge is another movable bridge where a center span rises vertically to allow maritime traffic to pass underneath. In contrast to the rolling bascule design, this bridge design introduces a vertical clearance restriction. As described in the title, this bridge design incorporates a 170-foot bridge span which ultimately limits the horizontal channel width for maritime traffic in the Norwalk River. Because of this, the design also introduces a greater impact to rail service than the preferred alternative.
The 240' Vertical Lift Span bridge design meets the Project's Purpose and Need by incorporating innovative engineering and construction techniques and technologies that allows the bridge to be more resilient and withstand extreme weather, load and external forces.
Shortest Overall Construction Schedule
This design allows for new bridge foundations to be built outside of the existing bridge foundations, which permits the current bridge to be operational for a longer period during construction. The 240' Vertical Lift Span bridge design has the shortest construction schedule of the movable bridge alternatives and is estimated to take approximately 4-5 years to build.
No Extended Navigation or Rail Restrictions
The vertical lift design allows for the new bridge to be built in pieces so that two-tracks on the New Haven Line remain operational throughout construction with only two weekend track outages. The towers, as seen in the renderings, are built around the existing swing span, allowing rail service to remain largely unimpeded.
Read more about the 240' Vertical Lift Bridge on the project page.