McCook County, South Dakota, is about 30 miles northwest of Sioux Falls. Interstate 90 runs through the rural county, which is home to nearly 6,000 people. The longest east-west highway in the country, I-90 runs from Seattle to Boston. The South Dakota Department of Transportation (SDDOT) is wrapping up a project on the route that runs through McCook County.

This section of I-90 is four lanes with two in each direction and a 50-foot grass median. The average daily traffic count is approximately 6,500 vehicles, with 25 percent of it being trucks.

The existing asphalt on the 15-mile stretch of interstate where the project is taking place is approximately 15 years old and is not bad condition, according to Rick Brandner, a Project Engineer for SDDOT. However, the asphalt was laid over concrete and that concrete is breaking up under the surface. This has become an issue, especially in hot summer months.

“It got too expensive and time-consuming to go out and repair I-90 during the summer,” Brandner says. “The department determined it would be wiser to remove the pavement and upgrade it to today’s standards.”

The team will remove the existing 4.75-inch asphalt surfacing and 9-inch concrete base and replace it with 11.5 inches of concrete throughout the entire length of the project. This project is focused on the westbound side of I-90, as the eastbound side was reconstructed last year.

While the issue exists beyond the 15 miles, SDDOT choose the McCook County line as the natural endpoint. “It’s a lot to do in one year,” Brandner says.

Other major project elements include removing and replacing a box culvert and two bridges. One of the bridges experiences severe flooding due to the East Vermilion Lake, which has led it to have scour issues. Because of the soil erosion around the foundation, the team determined that the footings were not deep enough. The second bridge had similar, though less severe, issues.

The SDDOT did a cost analysis and determined it was more cost-effective to install a new bridge. While the new bridge will be on the same footprint, it will have a wider mouth, deeper footings, and the columns will be on the bank rather than in the river.

To ensure the bridges are secure, the team needs to get below the scour. They put in cofferdams to work underwater. The area is home to glacial boulders that are being removed so the team can drive sheet piles. While SDDOT expected some boulders, there’s more than they anticipated.

“We ran into some boulders, which required us to stop driving,” Brandner says. “We had to get an excavator down there to remove big chunks of rock.” This process led to some delays.

Among the other challenges the team has encountered are supply issues from cement to innocuous items such as stainless-steel ties.

The project began mid-March 2022 and had an interim completion date in November 2022. The final striping was to occur in the spring of 2023, and the final completion was set for June 2023.

The team missed the interim completion date. When the construction season reopened in 2023, the contractor had approximately two more weeks of work left to accomplish. Among the work that they are completing is the installation of rumble strips in the shoulders. Brandner expects the team to be on time for the final completion this month. “This project was a lot of work and we had to be aggressive to complete 15 miles in one year.”

To make up for the project challenges, the team worked nights. SDDOT moved traffic to the eastbound side with one lane in each direction.

Michels Road & Stone, Inc, which is headquartered in Wisconsin, served as the general contractor. Brandner was satisfied with the large firm. He said they utilized some out-of-the-ordinary methods, such as stockpiling granular material onsite rather than offsite. “This saves money and time as it means reduced transportation costs,” Brandner says.

The construction budget for the project was $37.5 million, and it was paid via the traditional 80/20 split between the federal and state governments. The project is slightly over budget due to the installation of the cofferdams and the additional night shifts.

Another issue adding to the budget is that the plans were a bit old and things have changed on the ground since they were developed. This was due to a mini project that took place in the area in the interim. The team had to drain some ditches and build a berm next to a recently installed sewer lagoon. Ultimately, there was approximately $1 million added to the construction budget.

With the project set to complete, drivers will enjoy a smooth ride. SDDOT will be free to focus maintenance time and money on other areas. The new road has a 30-year life expectancy – plenty of time for crisscrossing the country or getting around McCook County.