A $47.8 million project in Bismarck, N.D., will replace a 61-year-old Diamond Interchange on I-94 built when Bismarck was still expanding. Work on the new interchange known as a Single Point Urban interchange or SPUI is in its second and most challenging year, said Bernie Southam, project engineer of North Dakota Department of Transportation (NDDOT).
"The time frame is a big challenge on this," Southam said. "Because the first year was the bridge embankments and the pier and abutments got built, and some dirt work with some temporary loops was done. So that year was easy. The second year is full of work and traffic changes it's a tight schedule to get done this season."
Ames Construction, based in Burnsville, Minn., broke ground on the project in May 2024 with a winter suspension from November 2024 through April 2025. Ames is responsible for the structure and dirt work, salvaged base, storm drain and culverts.
Subcontractor Northern Improvement Company of Bismarck won the bid for the concrete and asphalt paving, curb and gutter, sidewalk and concrete medians. Other subcontractors include Edling Electric of Bismarck; 3D Specialties/Dakota Fence; and J&L Steel Erectors.
North Dakota DOT photo
The existing interchange was built as a rural diamond interchange in 1964 with a roadway width of 24 ft. The exit and a portion of the Bismarck Expressway/ Centennial Road was reconstructed in 1995. The original 1964 structure was widened to the west into a 5-lane roadway with a 10-ft. pedestrian walkway. But in the 1980s a "major" truck stop was built just southwest of the interchange. Today, the interchange sees an average of 25,700 vehicles per day, 9 percent of which is truck traffic.
"The traffic on this roadway is pretty much local," Southam said. "The truck stop brings in people that are driving west and eastbound on the interstate to come in and fuel up and get lunch and overnight. But other than that, this is generally an urban expressway."
The new modified SPUI will "efficiently move large volumes of traffic by converging traffic under one set of traffic signals," Southam said.
The new interchange will feature parts of both a cloverleaf and diamond interchanges. It will have four traditional-style ramps like a diamond, but on also two cloverleafs on the eastside.
"The cloverleafs are fit inside the traditional looking ramps. The cloverleaf for eastbound traffic is an exit ramp and the one on the north side is a westbound onramp," Southam said. "The cloverleaf on the northside completely eliminates the left-hand turn motion for northbound traffic to go west. That was the big conflict point on this whole entire intersection because of all the truck traffic stop."
North Dakota DOT photo
Crews are maintaining traffic through the interchange during construction with traffic currently using the old roadway. During the next phase, traffic will be rerouted onto the new roadway, Southam said.
Work scheduled for completion by the end of the construction season, Nov. 25. includes:
• construction of the new eastbound entrance ramp;
• construction of the new eastbound exit ramp;
• construction of the new structure;
• construct new crossroad connecting Bismarck Expressway to the south end of the new bridge;
• construct new crossroad connecting Centennial Road to the north end of the new bridge;
• construct the northeast exit ramp and southeast loop ramp and deceleration lane;
• construct southeast entrance ramp and northeast entrance loop and acceleration lane; and
• traffic is using new bridge, new crossroad and new entrance and exit ramps as well as loops.
The 2026 construction season will be largely cleanup work, Southam said. Funding for the project came primarily from federal funds along with state and city dollars. It is scheduled for completion in summer 2026. CEG
