Over the past two years, the country has witnessed a surge of tunnel construction projects. The work has not involved band-aid repair to failing pipes or bridges, but it has been massive, strategic investments in tunnel infrastructure nationwide.
According to Tunnel Business Magazine, there are roughly 30 large tunnel projects across the country in various stages of planning or execution currently, and these efforts total nearly $50 billion in value.
The motivating factor for all the tunnel activity is not driven solely by aging infrastructure. Tunnel projects are increasingly justified because of extreme natural events, such as severe rainfall, flooding, and sea-level rises. Additionally, urban density and land scarcity are creating demand for tunnels as underground expansion has become one of the remaining options for transit authorities, utilities, and flood-relief conduits. Next-generation tunnel boring machines have improved modeling and lowered risk and cost making tunnels attractive options for stormwater storage, wastewater management, utility lines, fiber optics, and flood control prevention.
Upcoming projects in the planning stages outlined in this column are ones that allow ample time for contractors to begin preliminary pursuit efforts.
Officials at the Northeast Ohio Regional Sewer District have announced a $260 million project to construct a critical new tunnel to protect water purity. The project is a major component of a long-term effort to reduce overflows into Lake Erie and its tributaries. Located in Cleveland and Brooklyn within Cuyahoga County, the new tunnel will be designed to provide critical storage and to increase the flow capacity for the existing system.
The project calls for a deep rock storage tunnel to prevent sewer flows during wet weather events. By controlling overflows along tributaries, the tunnel will significantly improve water quality and reduce flooding. Once operational, the tunnel will also protect aquatic ecosystems and public health. Construction solicitations are expected in late 2026.
Sound Transit, Seattle’s public transit authority, will oversee a project to expand light rail service from downtown Seattle to nearby neighborhoods by constructing a new light rail tunnel. The extension will connect dense residential areas while improving mobility and transit frequency for Seattle’s growing neighborhoods.
Project leaders estimate the light rail work will cost approximately $814 million. This estimate includes about eight miles of total service, with more than three miles of tunnel running through the downtown area. The project will add nine new stations spanning downtown Seattle to uptown neighborhoods. Early plans indicate seven of these stations will be subterraneous.
Currently in the planning and environmental review phase, the design phase is expected to begin in 2026. Construction is scheduled for 2028. More information about a construction-solicitation release will be available once design is underway.
State officials with the Michigan Department of Transportation (MDOT) are preparing to launch a major drainage tunnel in Detroit. Estimated to cost up to $200 million, the tunnel will provide long-term stormwater management for one of the region’s most heavily traveled freeways.
Work will include the construction of an approximately 6,000-foot-long relief tunnel. It will provide about eight million gallons of storage capacity and will be designed to mitigate the impact of a 24-hour storm event. The scope of work includes tunnel work, junction chambers, drop-shaft bulkheads for future drainage connections, and surface restoration including street reconstruction. Once completed, the new tunnel will improve stormwater management, reduce flooding risk, and solidify the resilience of the I-94 corridor.
MDOT’s project will be delivered through a design-build model. An RFQ is slated for release in late 2025 and construction is scheduled to begin in 2026.
Design work is underway for a $2.1 billion project that will be overseen by the Massachusetts Water Resources Authority. The effort will be to deliver a water tunnel to provide resiliency for Greater Boston’s water system. The project will provide full redundancy of the metropolitan water tunnel system and allow the old system to be taken offline at any time for inspection, maintenance, and repair.
The program calls for roughly 15 miles of deep, hard-rock tunnels. It will deliver a five-mile North Tunnel terminating in Waltham and a 10-mile
South Tunnel ending in Mattapan. Together, the new tunnels will provide full redundancy for the 80-year-old Metropolitan Tunnel System. Tunnel Boring Machine (TBM) technology will be used for excavation and when this is completed, the tunnels will be lined with concrete. Other project components include the construction of 13 shaft sites that will have large launch- and receiving-shafts up to 500 feet deep. Smaller connection shafts will link to existing pump stations and mains. Early enabling work, such as shaft power supply and site demolition, will begin in 2026. Construction work on the South and North tunnels is slated for 2027 and 2028, respectively.
City officials in New York are moving forward with plans to construct a storage tunnel to reduce sewer overflow discharges into Flushing Bay. The $1.61 billion tunnel project is part of a larger combined sewer overflow initiative.
Work will include construction of a deep storage tunnel and a dewatering pump station that extends 2.5 miles with an anticipated diameter of roughly 20 feet. When completed the tunnel will have the capacity to store approximately 25 million gallons of water. Alongside the planned tunnel, the project will also construct a dewatering pump station to move overflow from the tunnel to the Bowery Bay Wastewater Treatment Plant. The design’s objective is for water to flow into the tunnel beneath highways and complex ramp systems through connecting sewers. The final alignment, shaft locations, and sizing of the tunnels and dewatering pump station will be determined once the design phase is finalized. Construction is slated to begin in July 2026.
Project officials are planning a deep storage tunnel to capture CSOs that discharge to the river in St. Louis. This project is a part of a broader long-term program to reduce wastewater overflows and improve water quality citywide.
Extending approximately six miles with an 18-foot inside diameter, the tunnels will contain wastewater and move groundwater out. The project will construct 6 shafts that connect multiple CSO outfalls to the main tunnel and large tunnel boring machines will be required to excavate deep underground and cut through bedrock. A dewatering pump station will support operations by pumping stored CSO from the tunnel back into the treatment system after storms, helping return capacity for the next event. Final details and sequencing will be confirmed during design.
Construction is anticipated to begin in late 2027 or early 2028. The entire wastewater is currently estimated at $2.3 billion, while the tunnel project is estimated at $178 million.
Tunnel construction calls for specific types of expertise and various types of equipment, but with every project, there are other components that usually involve subcontracting firms. These projects are large, and competition will be significant, so early pursuit strategies are critical.
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