South Dakota’s Interstate Highway Network.
Due to the low population density, the road network is not very extensive. In particular, there is a contrast between eastern and western South Dakota, with the Missouri River forming the dividing line. West of the Missouri River, the road network is much thinner, and many minor roads are unpaved. In the east is a denser road network due to intensive agriculture. The Missouri River and its reservoirs are an obstacle to east-west traffic, the number of river crossings is relatively limited, especially in the northern half of the state.
- Bittranslators: State overview of South Dakota, including geography, economy, population and history as well as introduction to major cities of South Dakota.
The state highway authority is the South Dakota Department of Transportation, abbreviated SDDOT. South Dakota has 132,657 kilometers of road, but the state has relatively decentralized road management, the SDDOT is responsible for the 12,598 kilometers of state highways, which include the Interstate Highways and US Highways.
SDDOT has its origins in the State Highway Commission which was established in 1913. In 1917 this merged into the larger South Dakota Highway Department. In 1973 this merged into the larger South Dakota Department of Transportation.
The Bureau of Indian Affairs (BIA) also manages roads in Indian reservations in the western part of the state. These are numbered separately.
- Deluxesurveillance: Nickname of South Dakota as The Mount Rushmore State. Also covers geography, history, economy, politics and administration of the state.
A small number of Interstate Highways traverse South Dakota. Interstate 29 forms a north-south route through the east of the state, from North Sioux City through Sioux Falls to Fargo and Canada. Interstate 90 forms a long east-west route through the south of the state, handling most of the tourist traffic to the national parks and Black Hills in the southwestern part of the state. Interstate 190 is a spur of I-90 in Rapid City, and Interstate 229 forms a bypass of Sioux Falls.
A number of US Highways traverse South Dakota. Unlike in North Dakota, more eastern states and Nebraska, there are hardly any US Highways in South Dakota that are designed as 2×2 divided highway. The only longer 2×2 road is US 12 between Aberdeen and I-29 for about 75 miles. Elsewhere it is no more than short approach roads equipped with 2×2 lanes. US 12 is also the main east-west route through the north of the state, while US 14 and US 18 serve the center and south of the state. The US 83 forms the north-south route in the center of the state, and is the main link to the capital Pierre and is equipped with 2×2 lanes between I-90 and Pierre for about 50 kilometers. US 281 forms a north-south route through the eastern half of the state, passing through Aberdeen. US 85 forms a north-south route in the far west of the state and is a major route to the North Dakota oil fields.
- US 12 Summit – Aberdeen 121 km
- US 83 Vivian – Pierre 51 km
- US 281 Aberdeen – Mellette 34 km
- SR-37 Mitchell – Huron 85 km
- SR-50 Vermillion – Yankton 56 km
- SR-79 Rapid City – Buffalo Gap 82 km
A network of state highways forms the secondary road network. This is denser in the east of the state than in the west of the state, where many minor roads are unpaved. Even numbers run east-west and odd numbers run north-south, as for the one- and two-digit numbers. The three digit numbers are more randomly assigned. The numbering runs from 10 to 473, with two separate numbers, 1804 and 1806. Many numbers are skipped. No state highway is a freeway, but a number of state highways are designed as a 2×2 divided highway, most prominently SD 37, SD 50 and SD 79.
There are no toll roads in South Dakota, nor have there ever been.
Like many states on the High Plains, South Dakota had hardly any paved roads until the 1920s. In 1913, the State Highway Commission was established to map out which roads needed improvement. This was merged into the State Highway Department, a department of South Dakota, in 1917. After the Federal Aid Road Act of 1916, federal money became available for the development of the road network. In 1919, the first federal funding was used to develop a road in Codington County in the northeast of the state as a gravel road. In 1922, a fuel tax introduced to finance the development of the road network. In 1924, the first bridge over the Missouri River opened at Mobridge, connecting western and eastern South Dakota. In the 1930s the main roads were asphalted.
Before the creation of the Interstate Highway system in 1956, South Dakota did not have a single highway, which was not necessary in this sparsely populated state. The construction of the motorway network started in the late 1950s and a large part of the motorway network was opened up during the 1960s. The state’s first highway opened in 1958. I-190 and I-229 opened to traffic about 1962. By the late 1960s, most of it had been completed, although there were still two missing links for quite some time, for example, I-90 between the Wyoming and Spearfish border did not open to traffic until 1978, and I-29 followed around Sisseton in 1983.. Because the traffic intensities in these regions are very low, this was not a significant problem.
There is absolutely no congestion in South Dakota. The highest traffic volumes are around 45,000 vehicles in Sioux Falls.