The Vermont Agency of Transportation (AOT), in collaboration with the Town of Middlebury, replaced two nearly 100-year old rail bridges in the center of Middlebury with a tunnel in the summer of 2020. The 360-foot tunnel that replaced the Main Street and Merchants Row bridges addresses several deficiencies. The tunnel provides vertical clearance for double-stack rail cars. By lowering the rail bed approximately 4', clearance has increased to 21' without impacting the grade of the road and sidewalks above. The tunnel provides improved rail alignment, softening the rail curve to allow better horizontal clearance for trains. The project includes drainage improvements, mitigating the risk of icing problems as well as ponding that occurred historically.
The two bridges were about 300 feet apart, with one located on Main Street/VT 30 and the other on Merchants Row. For over 25 years, AOT bridge inspection reports documented ongoing deterioration of both bridges. Concrete cracking, delamination, and spalling had degraded all bridge components. Embedded steel reinforcement was rusted and exposed. There was leakage through the deck and full depth holes on the Merchants Row sidewalk, requiring patching.
In the spring of 2017, AOT became increasingly concerned about the deteriorated condition of the sidewalks and concrete that fell onto the railroad tracks. A sudden, unplanned emergency resulted in downtown Middlebury road closures for several months. The Agency decided to replace both bridges with temporary bridges in the summer of 2017, until permanent structures were built. Both the Main Street and Merchants Row bridges were demolished and travel was restored within four weeks.
The replacement of the bridges with a tunnel is a notable engineering and design feat within Vermont. After three years of construction, Middlebury stakeholders celebrated the process. Although the major 10-week closure is completed, the team will continue work task into 2021.
Many considerations shaped the planning and design of the project. The design team balanced community needs and development character, local and regional mobility, construction feasibility – all while keeping the rail line active, except during the closure period. Communities along the line depend on rail for deliveries of various commodities.
Among (though not all!) the items the project team has focused on are:
- Placing utilities in the Printer’s Alley underground so that they do not interfere with the crane that constructed the tunnel
- Acquiring Right-of-Way, both temporary and permanent
- Negotiating with Vermont Rail Systems about feasible work windows that enable construction to get done without interrupting rail service
- Monitoring walls, foundations, and windows of nearby historic buildings during activities that may produce vibrations
- Monitoring noise during construction
- Designing the project to mitigate risk from the 100-year flood level of Otter Creek
- Supporting a design that considers community character and aesthetics
- Creating a safe working environment for workers, motorists, and the community
- Scheduling a construction sequence to minimize community disruption
- Developing a communication and outreach program to identify and respond to community concerns
Before construction, AOT conducted an Environmental Assessment in accordance with the National Environmental Policy Act. The Final Environmental Impact Statement concluded with a Finding of No Significant Impact.
Replacing the rail bridges with a tunnel received broad support at public meetings and was endorsed by the Middlebury Town Selectboard. The tunnel changes the town landscape by overlaying the depressed, walled rail bed with green space that links Triangle Park with the Village Green in the heart of downtown.