Editor’s note: A version of this story appeared as an opinion column in the Duluth News Tribune on January 28, 2026.
An immersed tube is an underwater tunnel composed of several prefabricated segments, constructed on dry land, and then floated to a construction site. This construction site is a trench dug into layers of clay, mud and silt. The trench floor is reinforced with gravel to hold the weight of the tube, much like constructing a road. Once sunk into the trench, these tubes are then linked with watertight seals and buried for protection from strong currents and sinking ships. As these tubes are constructed in a shipyard setting, these tubes are considered the cheapest and safest type of tunnels.
I propose an immersed tube holding two tracks for trains and a 20-foot-wide pedestrian and bicycling lane under the St. Louis River in the Twin Ports.
In Antwerp, Belgium, engineers are building on dry land immersed-tube sections to create a six-lane, immersed-tunnel highway under the wide Scheldt River. To one side of this tunnel would be a 20-foot-wide bicycling and pedestrian path. I can imagine how happy local walkers and bicyclists would be to have a tunnel like this to walk and bicycle in between Duluth and Superior.
These tubes could be sunk between Rices Point and Connors Point. A second immersed tube could be built at Grassy Point, replacing the aging Grassy Point Swing Bridge. Constructed by Fraser Shipyards workers, making steel or reinforced concrete tubes would provide high-paying jobs for people, their wages creating jobs inside and outside of the construction industry. The next generation of skilled construction workers also could be educated.
Examples of immersed tubes include the completed 63rd Street Tunnel under the East River in New York City and the under-construction Fehmarnbelt tunnel under the Fehmarn Strait connecting the Bay of Kiel and the Bay of Mecklenburg in the western part of the Baltic Sea between the German island of Fehmarn and the Danish island of Lolland. As these German and Danish tube segments are 712 feet long, it would take two segments to reach across the ship channel between Rice’s Point and Connors Point.
By bypassing the Grassy Point Swing Bridge, using the Rice’s Point and Connors Point connection would save 15 minutes off Northern Lights Express (NLX) travel times between Duluth and Superior. The NLX is the proposed passenger train between the Twin Ports and Twin Cities.
An immersed tube between Duluth and Superior is possible and would benefit future NLX riders, walkers, and bicyclists. This tube tunnel also would provide another Duluth-to-Superior route for freight trains.
Midwesterners’ fight for better and more frequent transit options for transit-underserved communities doesn’t end.