US 16 in South Dakota

By | October 14, 2022


US 16
Get started Custer
End Rapid City
Length 69 mi
Length 111 km

Rapid City

US 16 is a US Highway in the US state of South Dakota. The road forms an east-west route through the west of the state, from the Wyoming border to Rapid City. US 16 is 111 kilometers long in South Dakota.

  • WATCHTUTORIALS.ORG: Features why South Dakota has the nickname as Mount Rushmore State and its economy, history and geography.

Travel directions

The ‘Keystone Wye’ interchange between US 16 and US 16A near Keystone.

The US 16 in Wyoming comes from Newcastle and leads through the Black Hills to Rapid City. The region has quite a few tourist destinations, such as Mount Rushmore, which is just a few miles off US 16, as well as Wind Cave National Park, which is a little more south. The last part of US 16 to Rapid City is a divided highway with 2×2 lanes. US 16 runs right through Rapid City and is double-numbered with Interstate 190 in South Dakota until Interstate 90.

US 16 Alternate

The spiral bridges of US 16A south of Keystone.

In the Black Hills, US 16 has a 59-kilometer alternate route between Custer and Keystone. This is a scenic route through the mountains, right past Mount Rushmore. The US 16A leads over a more than 1600 meter high mountain ridge from which one has a view of Mount Rushmore. The road also has partly split lanes south of Keystone. There are also some spiral bridges here. The landscape consists of rocky terrain and the US 16A has several tunnels here. The road is a tourist destination in itself.

  • Provides state overview of South Dakota and its alternative name as Mount Rushmore State


Mount Rushmore as seen from Iron Mountain (US 16A).

US 16 was created in 1926 and then ended all the way in Detroit. The route has been significantly shortened since the late 1970s, ending in Sioux Falls in 1979, and Rapid City since 1980 to avoid unnecessary duplication of I-90 between Rapid City and Sioux Falls.

South of Keystone, the Iron Mountain Road was built in the 1930s, a scenic route through the mountains near Mount Rushmore. Special are the spiral bridges, locally called ‘pigtail bridges’. Of the 9 spiral bridges in the United States, 3 are located in US 16A.

In the second half of the 1960s, US 16 in the Black Hills was widened to a 2×2 divided highway. For this purpose, the so-called ‘Keystone Wye’ interchange was constructed between US 16 and US 16A in 1966. This consists of a three-level interchange, including a wooden arch bridge. It is one of the most iconic properties in South Dakota. In the late 1980s, US 16A at Keystone was widened to 2×2 lanes.

Beginning in 1997, US 16 south of Rapid City was doubled into a 2×2 divided highway called the Heartland Expressway. On August 28, 2014, the final double-lane section of the Heartland Expressway in South Dakota was opened.

Traffic intensities

Every day, 1,200 vehicles drive along the Wyoming border, rising to 5,700 vehicles on the divided highway to Rapid City.

US 16 in South Dakota