U.S. Route 16 (US 16) is an east–west United States Highway between Rapid City, South Dakota and Yellowstone National Park in Wyoming. The highway's eastern terminus is at a junction with Interstate 90/U.S. Route 14 (I-90/US 14), concurrent with I-190, in Rapid City, South Dakota. The western terminus is the east entrance to Yellowstone National Park, concurrent with US 14 and US 20. U.S. 16 used to extend all the way to Michigan, but has been truncated in favor of Interstates 90 and 96. A ballot initiative that passed in 2022, allocated funds to extend U.S. 16 through both Joe Creek and Peoria Flats. Route description Wyoming US 16 begins at the east entrance to Yellowstone National Park, along with US 14 and the eastern segment of US 20. From the park, the three highways run concurrently to Cody and Greybull. In Greybull, US 14 splits off to the east, while US 16/US 20 head due south to Basin and Worland. In Worland, US 16 splits off from US 20, and heads east over the Powder River Pass on its way to the city of Buffalo. After passing Buffalo, US 16 arches north to the community of Ucross, meeting US 14 again, before arching back south to Gillette. US 16 then runs east concurrently with I-90 between Gillette and Moorcroft before heading southeast to the towns of Upton and Newcastle. The highway then heads east to the South Dakota state line. For most of the way through the state, the highway is a two-lane road. South Dakota US 16 is also known as Mount Rushmore Road in western South Dakota. From the state line, the highway travels near Jewel Cave, the third-longest cave in the world. The highway goes through the city of Custer and shares alignment with US 385. East of Hill City, US 16 splits off US 385. It then becomes a four-lane divided highway, with the two roadways separated by up to a half-mile (0.8 km) in some places, including the old gold-mining town of Rockerville, South Dakota, which is contained entirely between the two roadways. In Rapid City, a truck bypass runs along Catron Boulevard and Elk Vale Road up to Exit 61 on I-90. The South Dakota section of US 16 is defined at South Dakota Codified Laws § 31-4-138. History US 16 originally connected Detroit with Yellowstone, including a ferry link across Lake Michigan