Located on the Missouri River, North Dakota’s capital city of Bismarck is home to just over 77,000 residents and only three interchanges. One of those interchanges — located at Exit 161 on the I-94 interchange — is undergoing a reconstruction. The North Dakota Department of Transportation (NDDOT) and general contractor, Ames Construction, are leading the project.
Constructed in 1964, the original interchange was part of the Interstate 94 system. It was a rural diamond interchange with a roadway width of 24 feet.
The Bismarck/Mandan urban area has experienced consistent growth since the interchange's construction, particularly in the ‘80s and ‘90s.
To compensate for the growth, a portion of the Bismarck Expressway/Centennial Road from Miriam Avenue to Trenton, and the Exit 161 interchange, were reconstructed in 1995.
NDDOT widened the original 1964 structure to the west into a five-lane roadway with a 10-foot pedestrian walkway. City officials converted Bismarck Expressway/Centennial Road into an urban roadway with curb, gutter, and sidewalk.
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A major truck stop constructed just southwest of the interchange brought more change to the area in the late ‘80s. In the early 2000s, the Bakken Shale oil boom led to significant growth in the area.
In 2020, the average daily traffic in the area was 25,700, and NDDOT projects it to reach 33,320 in 2040. Trucks make up 9 percent of the traffic.
"The increase in traffic and closeness of Miriam Ave. to the interstate limits the amount of storage possible for left-turn movements," said Bernie Southam, a Transportation Engineer for NDDOT, who is overseeing construction for the state.
"During the busy parts of the day, the left-turn lanes would back up onto the inside through lane, causing the traffic service level of the interchange to drop to a lower level of service," he added.
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KLJ performed a traffic operations study and found that if the interchange is not improved by 2045, “many of the traffic movements through the study area are expected to operate at an unacceptable level of service E or F.” According to SMATS, a company specializing in smart transportation data collection and analysis, Level F service would mean that the "control delay is over 80 s/veh [seconds per vehicle] or the volume-to-capacity ratio is higher than 1.0. Typically assigned when progression is very bad and there is a long cycle length. Most cycles are not able to clear the queue."
The delays affect drivers heading north and south, causing traffic to back up to another major intersection to the south.
"The level of service frustrates drivers and is at a level where something needed to be done to improve it," Southam said.
To alleviate the traffic congestion at the interchange, the team is installing a modified single-point urban interchange (SPUI). The interchange is modified because of the addition of two cloverleafs. After working with the public, local business owners, and the city, NDDOT determined that a modified SPUI was the best option.
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The department’s website says that SPUIs are known to "efficiently move large volumes of traffic by converging traffic under one set of traffic signals." They also improve safety by eliminating or reducing conflict points. The modified SPUI the team is installing has two traffic signal locations.
In this case, the modified SPUI will remove two left turns, which become right-turn movements via the provided cloverleafs.
The northeast cloverleaf will allow northbound traffic on Bismarck Expressway/Centennial Road to enter westbound I-94, utilizing a right-turn movement. The left-turn movement to I-94 was eliminated.
The southeast cloverleaf will allow eastbound I-94 traffic to exit I-94 and enter northbound Bismarck Expressway/Centennial Road. The cloverleaf eliminates a left-turn conflict with southbound traffic. It also creates Bismarck/Mandan's first interchange with an A and B exit.
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Finally, a bridge is also part of the SPUI. The 270-foot-long bridge features decorative elements, including imprinted rock patterns on the pier columns and cap, a crash barrier, and decorative columns on the bridge deck.
Work on the project began in spring 2024 and is scheduled for completion in summer 2026. The bulk of the work is taking place in 2025.
Southam said the 2025 construction season has been tight. The typical construction season in North Dakota runs from mid-April to mid-November.
"We could experience freezing temperatures in this area by November, which impacts our ability to get work done," Southam said, "so we need to make sure we're on schedule or even early."
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NDDOT split the project into three phases, then split the second two phases into three more phases. The many phases have also required numerous traffic control layouts. NDDOT hired a public relations (PR) firm to keep the public informed about the changes in traffic.
The PR firm issues news releases that local radio stations pick up. Another way the message gets out is via local news stations. There are also digital message signs to alert the driving public about the changes to the traffic patterns.
The constantly changing traffic patterns could impact worker safety. Ames Construction regularly reminds the team to stay alert and be careful.
"They have safety meetings every morning to remind the crew about changes and to ensure they don't get complacent," Southam said.
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In areas where there is no place to escape an oncoming car, there are portable concrete barriers to separate the crew from traffic.
Another challenge is getting construction materials to the work zone. Since the interchange already has a poor service level, adding traffic to the area would make it worse. A slowdown in getting the materials to the work zone would impact the schedule.
The contractor has used a temporary dirt road — which will be part of the loops on the cloverleaf — as a way to hasten material delivery. By using the dirt road, the contractor eliminated the need to make left-hand turns.
"If they had not used the dirt road, construction vehicles would have needed to go to the next interchange and turn around to bring materials to the site," Southam said.
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The team has used concrete pavement breakers on the job. Southam noted that the self-propelled, remote-controlled vehicle has heavyweight trip hammers that fracture the road every 2 feet. It makes for a quicker and cleaner process of removing the road.
Based in Burnsville, Minnesota, Ames Construction has worked with NDDOT previously. According to Southam, they are well-known for building bridges.
The project has a budget of $47.5 million. The federal government is the primary funding agent for the project (81 percent), while the state (9 percent) and city (10 percent) are paying the remainder. The project is on budget so far.
"There have been no major changes, and we're working with a good set of plans," Southam said.
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He further credited the design team (an internal NDDOT team) for being “responsive and getting answers back to the contractor quickly.” The hasty responses have also helped keep the project on schedule.
"There were times this summer when we were behind schedule, but the contractor made changes to gain time back," Southam said.
Ames intends to bring in more personnel for the next phase to keep the project on schedule.
When the team completes the modified SPUI along I-94, the interchange will see dramatic safety and function improvements. The new interchange will also allow for future growth of traffic along the roadway.
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"Our goal is to get to Level A service, and I'm confident that the interchange will make it," Southam said.
- Owner/Designer/Engineer: North Dakota Department of Transportation
- General Contractor: Ames Construction, Burnsville, Minnesota
- Other Contractors: Northern Improvement Company, Bismarck, North Dakota; Edling Electric Inc., Bismarck, North Dakota; 3D Specialties/Dakota Fence, Fargo, North Dakota; J&L Steel Erectors, Savage, Minnesota
