Located at a strategic point along the western part of Lake Superior, the Duluth, Minnesota, and Superior, Wisconsin, metropolitan area is known as the Twin Ports. As North America's farthest-inland freshwater seaport, more than 2,300 miles west of the Atlantic Ocean, the Twin Ports are among the United States' larger cargo ports and are the cargo capital of the Great Lakes. As such, the Duluth/Superior ports provide a multimodal shipping hub from which to transport goods through the Great Lakes-St. Lawrence Seaway System and on to the East, West, and Gulf Coasts along rail lines and major highways.
In the heart of Duluth, adjacent to Lake Superior's St. Louis Bay, the Twin Ports Interchange (TPI) is the point of convergence for three high-volume highways — Interstate 35, Interstate 535, and Highway 53. A busy system-to-system interchange, it carries a high volume of commuters and is a first- and last-mile connection to the Duluth Port Terminal's intermodal facilities for highway, rail, and waterway freight. The interchange experiences an average of 80,000 vehicles each day, of which 5,320 are classified as heavy commercial.
Since its construction in the 1960s, however, the Twin Ports Interchange has become a confusing array of multiple road levels and ramps. The original design utilized elevated roadways and ramps due to the poor condition of the foundation soils. Non-redundant bridges — which have the potential to fail immediately under local damage, such as loss of load carrying elements — and structurally deficient bridges have resulted in overweight truck detours. Additionally, the interchange has the third-highest crash rate in the state of Minnesota.
Now that is changing, thanks to an extensive Minnesota Department of Transportation (MnDOT) project designed to provide a new road alignment along with updated infrastructure. The $435 million Twin Ports Interchange Project encompasses reconstruction of the I-35/I-535/Highway 53 interchange and adjacent roadways. This massive, multi-phase effort is designed to “untangle” the current system by relocating ramps, incorporating safety improvements, addressing weight restrictions on older bridges, and replacing aging infrastructure.
When complete, the Twin Ports Interchange Project will improve safety and traffic flow efficiency by:
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- Providing a new conventional design (eliminating left exits) by relocating all exits and entrances to the right side of the roadway
- Improving merging sight distance and eliminating merge conflicts
- Eliminating weaving problems near the interchange (by removing left exits)
- Providing lane continuity for through I-35 traffic (with two continuous lanes north and south throughout the project)
- Providing first- and last-mile connections with the Duluth Port Terminal
“Given its proximity to the port area of Duluth or Lake Superior, the Twin Ports Interchange is an integral and important part of having a functioning international port,” said Pete Marthaler, MnDOT Major Projects Engineer. “The interchange needs to be able to take high and heavy and long loads and put them straight on the interstate right away, as opposed to having to navigate some of the more local routes in order to bypass those deficient bridges.
“Eliminating blind merges and left exits is a primary component of the project. On the existing interchange, you would come up on a ramp and have to crane your neck around about 170 degrees to make sure no one was coming behind you from your left, in order to merge as needed while moving from I-35 to Highway 53 or coming from Highway 53 going onto Highway I-35.
“And, we've now got longer merge lines, so that one merge is completed before another one comes in.”
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In addition to interchange reconfiguration and geometric safety improvements, key project elements include: stormwater treatment and system improvements; geotechnical soil stabilization and load transfer platforms; utility relocations and improvements; creek realignments; and local roadway upgrades.
Planning for the TPI Project began in 2016, and initial construction on the project began in September 2020. The expected completion date is fall 2025.
The primary contractor is a joint venture between Ames Construction, based in Burnsville, Minnesota, and Kraemer North America, headquartered in Plain, Wisconsin. Alex Schulz, Ames-Kraemer JV Project Manager, pointed out that the TPI Project is just the latest teaming of the two firms.
“We are two locally based companies which typically have the same values, as well as strong local workforces and a proven track record of successfully completing projects together,” he said. “We've done multiple joint ventures so far.”
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The project is also utilizing over 100 subcontractors, engineering consultants, and suppliers.
The TPI Project and a planned adjacent project — the replacement of the John A. Blatnik Bridge — were two high-priority and concurrent MnDOT projects. The aging Blatnik Bridge, which opened in 1961, is one of two bridges which carries I-535 over the St. Louis Bay and is an important freight and commercial connection between the Twin Ports.
“From a funding standpoint, both projects could not be accomplished so close together in timeline,” Marthaler said. “So, the decision was made to accelerate TPI, so that by the time we did the Blatnik project there would be enough time separation, financially. So, the 535/35/53 interchange is being built first. The Blatnik project will probably launch in 2027.”
The TPI Project was originally structured to have four work packages, or phases, according to Marthaler.
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“However, due to budget limitations we encountered, we had to initially jettison two portions of the project,” he said. “Those two portions are the Garfield Interchange at the intersection of Garfield Avenue and 535, and the component of trunk Highway 53 that winds up the hill in Duluth. So, the packages that we had budget for, and with which we proceeded with in September 2020, were the I-35 corridor and the flyover bridges.
“However, with the infrastructure bill that was passed in 2021, we were able to add back the two other components and commence work on those in September 2022. We've been working on those last two portions since then.”
“One of the project's major goals was to figure out a way to keep northbound and southbound traffic moving on I-35 in both directions while construction was going on,” Schulz added. “So, the phasing during the first two to three years was greatly determined by how it affected I-35 mainline traffic.
“Simplistically, the first major phase was moving both directions of mainline I-35 traffic to the northbound side of the freeway. Crossovers and widenings were to accommodate these movements. Construction of the southbound freeway and overhead structures was completed during this time. Then it was flipped, with traffic being placed on the southbound side of the freeway while construction commenced on the northbound freeway and overhead structures.”
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Equipment utilized on the TPI Project includes Manitowoc cranes; MLC and American cranes; Tadano Mantis and Grove hydro cranes; and a variety of Caterpillar excavators, dozers, loaders, and graders.
As Marthaler pointed out, the current bridges along the mainline I-35 corridor are replacements for old low-level bridges.
“When they were built, the most economical way was to span over poor soils which existed — from both industrial fills and fills over marine or lake-shore wetland areas,” he said. “To build a traditional road embankment on there would never have worked, so when they did it in the early 60s, they built low-level steel girder bridges — pile bents with very simple pier caps. These bridges were only 5 to 10 feet off the ground.
“With the improvements in computer modeling and geotechnical information, we have employed a ground improvement solution, which allowed us to circumvent weak foundations and soil materials to improve bearing capacity and stability of the ground. On this project, we're using a Controlled Modulus Columns system. These are 15-inch grout cast columns that are poured into the soil. When assembled altogether and you put a low-transfer platform on top of it, you have a robust platform to put a roadway embankment on. This allows us to take out the low-level bridges and put them back on embankments.”
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A basic consideration when planning a project of this size and scope in Duluth is the topography and geology of the area, which can create multiple challenges for drainage and foundations. Other challenges ranged from the steep road grades which are common in Duluth, to the need to keep traffic moving on I-35 during construction.
“Something that made this project really challenging is that we were hemmed in between the urban environment of Duluth, two trout streams, and the adjacent railroad,” Marthaler said. “There's not a lot of room to move laterally within the project area.”
“The Ames-Kraemer JV team maximized winter work, such as bridge removal, pile driving, and construction of the substructure and Miller Creek box culvert so earth work, concrete pours, and paving could start in the summer months,” Schulz said. “The project also required management and treatment of contaminated soils and groundwater.”
One of the most challenging elements was the construction of a box culvert — which is combining two existing trout streams into one — under I-35 and the nearby railroad tracks, to empty into the St. Louis Bay. This new combined stream will add capacity and ease future flooding.
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“Building a cast-in-place box culvert, 505 feet long and 56 feet wide, that spans underneath an active freeway and an active railroad is very, very challenging, because you're trying to manage traffic from both elements, neither of which can be shut down,” Marthaler said. “The phasing was critical.”
According to Schulz, the grouted displacement columns were one of the innovative aspects of the construction process.
“The grouted displacement columns are fairly unique in their own regard, in the total operation, but in this project they have special significance due to contaminated water and contaminated soil being big issues,” he said. “The columns were essentially bored down into the ground and compressed the soil against the side of the shaft. So, the amount of spoil that came up from the shaft was very minimal. That limited — if not eliminated — the amount of contaminated soil that was produced.”
The comprehensive Twin Points Interchange Project will vastly improve a major corridor, benefiting both local traffic and the movement of freight and goods to and from an important port. The joint venture between Ames and Kraemer, in conjunction with MnDOT, is a key factor in the progress of this reconstruction of a critical interchange.
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“From a safety standpoint, I think it's a very good project that we were able to reduce the amount of bridge deck, because in our climate [and] in our area, those do ice over first,” Marthaler said. “Getting our main freeway corridor back on embankment is a substantial safety improvement, as is the elimination of those blind merges and left exits. Working with the Ames-Kraemer JV has been of the more fun projects in my career. Having a good project management team that works together is always appreciated.”
“I think the partnership between the joint venture and MnDOT has been a key point in making this project successful,” Schulz added. “We're glad and honored to be a part of such a key piece of infrastructure for not only the Duluth-Superior area, but the Upper Midwest.”
Photos courtesy of Minnesota Department of Transportation
