Interstate 90 or I -90 is an Interstate Highway in the U.S. state of South Dakota. The highway forms an east-west route through the south of the state, from the Wyoming border near Spearfish to the Minnesota border at Valley Springs. I-90 serves two larger cities, Rapid City to the west and Sioux Falls to the east. The highway runs for long stretches across the barren High Plains, but also loops around the Black Hills in western South Dakota. I-90 is 664 kilometers long.

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Travel directions

I-90 at Rapid City.

I-90 near Pierre.

I-90 in Jackson County in western South Dakota.

West of Spearfish, Interstate 90 in Wyoming crosses the border into the state of South Dakota at 1,080 meters above sea level. The highway then curves around the Black Hills and also runs partly north-south. There are two small towns in this region, Spearfish and Sturgis, and I-90 passes well south of Belle Fourche. The area consists of the barren High Plains, but to the south are the forested Black Hills. At Spearfish there is a short double numbering with US 85.

One then reaches the city of Rapid City from the northwest, which is the largest city on the route in western South Dakota, and is located on the edge of the Black Hills. Locally, I-90 has a short spur to Rapid City, Interstate 190. East of Rapid City is the large Ellsworth Air Force Base just off I-90. The highway runs east from Rapid City across the barren plains of the High Plains. This area consists of ranches and large farms, there is hardly any vegetation. US 14 branches off at Wall and runs parallel to I-90 to the capital Bismarck. Bismarck is well north of I-90 on US 83. I-90 runs along the edge of the Badlands of South Dakota but continues through very sparsely populated countryside. There are hardly any places larger than a hamlet on a long stretch of the route.

At Chamberlain one crosses the Missouri River, which is dammed up here in Lake Francis Case. I-90 descends very gradually from west to east from 1,000 meters at Rapid City to 500 meters at Sioux Falls. To the east, the area becomes less arid and agriculture becomes more intensive. However, the route of I-90 continues through sparsely populated area, only Mitchell is a somewhat larger village between Rapid City and Sioux Falls. Near Salem you cross the US 81.

I-90 then continues through the north side of Sioux Falls, the largest city on the route. There is a cloverleaf cloverleaf with Interstate 29 and Interstate 229 connects on the east side of Sioux Falls. Not much later, at Valley Springs, the border with the state of Minnesota follows. Interstate 90 in Minnesota then continues east toward Worthington and Albert Lea.

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Monuments and parks along the route

The main tourist destinations in South Dakota are on Interstate 90. From west to east, you pass the Geographic Center of the United States, reached via US 85 at Belle Fourche. The monument and the actual site are about 30 kilometers apart. After this, the highway passes through the Black Hills National Forest, a mountainous region that contains the only major forest area in the state. Near Rapid City one can go via US 16 to Mount Rushmore national monument, where the heads of the presidents are carved into the rocks. Also nearby is the lesser-known Jewel Cave National Monument, the second longest known cave in the world, with over 225 kilometers of cave systems.

A little further east, you’ll pass the Minuteman National Historical Site, a museum dedicated to a nuclear weapons control center that also houses a nuclear missile. This is part of a huge area the size of half the Netherlands where rocket launch silos were built in the past. Here you can also visit a National Park, namely that of the Badlands, a large park with ravines and gorges. Beyond that is a massive recreation area in the form of the Missouri River and the immense Lake Oahe reservoir, which begins halfway across the state and extends into North Dakota.

In the city of Sioux Falls you can find some entertainment in the form of Falls Park, a city park with many waterfalls, from which the name of the city comes, which is the River Sioux.

In the winter, driving on Interstate 90 can be tricky and even dangerous, especially during snow storms and temperatures that can drop below -30 degrees. There is an average of one meter of snow in winter, which often remains the whole winter. Especially on the open plains in the west, the strong wind can also be difficult for freight traffic.

History

I-90 was opened mainly during the 1960s. The first sections to be constructed were in the Rapid City region, and a stretch of about 30 kilometers between Wall and Interior. These were opened in 1961 or 1962. In 1962, a stretch opened between New Underwood and Wasta, just east of Rapid City, as well as the route through the Badlands, and from Sioux Falls to the Minnesota border. By the late 1960s, much of the route was completed. The final section, which began construction around 1975, was the route from the Wyoming border to Spearfish, which opened in 1978, completing I-90 through South Dakota.

Traffic intensities

Some 5,600 vehicles cross the border into Wyoming every day. This rises to about 20,000 vehicles at Rapid City, but drops to about 5,000 vehicles on the long stretch afterwards. East of the Missouri River is slightly more traffic, ranging from 7,000 to 10,000 vehicles. At Sioux Falls, the busiest section has 21,000 vehicles per day. 12,000 vehicles cross the Minnesota border every day.