U.S. Highway 16 (US 16) is an east–west United States Numbered Highway between Rapid City, South Dakota, and Yellowstone National Park in Wyoming. The highway's eastern terminus is at a junction with Interstate 90 (I-90)/US 14, concurrent with I-190, in Rapid City. The western terminus is the east entrance to Yellowstone National Park, concurrent with US 14 and US 20. US 16 used to extend all the way to Michigan but has been truncated in favor of I-90 and I-96.

Lengths

	mi	km
WY	471	758
SD	68	109
Total	540	870

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 heads due south to Basin and Worland. In Worland, US 16 splits off from US 20 and heads east over 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.

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 (0.80 km) in some places, including the old gold-mining town of Rockerville, 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.

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US 16 originally connected Detroit with Yellowstone National Park, including a ferry link across Lake Michigan between Muskegon, Michigan, and Milwaukee, Wisconsin. In Michigan, the route was in use long before automobiles and was known to white settlers as the Grand River Road, and prior to the designation of U.S. Highways in 1926, had been designated as M-16 in the 1920s from Detroit to south of Muskegon. In 1938, reflectorized discs were placed on US 16 every 100 feet (30 m) from Detroit to Lansing, resulting in fewer nighttime traffic accidents. Other states would later do the same on their roads.

US 16 initially crossed the South Dakota–Wyoming state line west of Spearfish. U.S. Highway 216 (US 216) was commissioned in 1930 as a loop off US 16 to the south between Rapid City and Moorcroft, crossing the state line west of Custer. In 1934, US 16 was moved to the US 216 alignment, while the former US 16 became part of an extension of US 14.

In Michigan, most of US 16 was superseded by I-96 and a segment of Grand River Avenue in Detroit ultimately became M-5. US 16 was later decommissioned in Wisconsin, Minnesota, and eastern South Dakota to its present termini.

Between Rapid City and Dexter, Minnesota, it has been supplanted by I-90. In Faribault County, Minnesota, the highway took on another number as there was already a county highway numbered 16. Residents of the county continued referring to the road as "16" or "old 16" and eventually the county renumbered it as County Road 16 (CR 16). From the county's western border with Martin County, US 16 continued east through the city of Blue Earth as part of 1st Street and Leland Parkway until it briefly combines with US 169/Grove Street. One-half mile (0.80 km) south of that point at the intersection of Grove and 7th streets, CR 16 followed 7th Street and continued east to the border of Freeborn County. Most of the stretch through Faribault County was a relatively narrow two-lane highway with wide gravel shoulders that has been widened at least two times since US 16 was decommissioned. East of Dexter, it is now Minnesota State Highway 16 and State Trunk Highway 16 in Wisconsin. In South Dakota, it was replaced by various state highways (including South Dakota Highway 38, or SD 38, and SD 248) and county roads: generally, in West River, the old alignment was transferred to county responsibility entirely, while, in East River, it remained a state-maintained highway.

An older US 16A in South Dakota has become SD 240.

In South Dakota in 2009, the South Dakota Department of Transportation designated US 16/US 385 between Custer and Hill City, which passes by the Crazy Horse Memorial, now being carved in the Black Hills, as the Crazy Horse Memorial Highway. This segment of US 385 is also a part of the George Hearst Memorial Highway.

Mileage resets at the state line crossing.

State	County	Location	mi	km	Destinations	Notes
Wyoming	Yellowstone National Park		0.000	0.000	Yellowstone National Park East Entrance	National western terminus of US 14 and US 16; western end of US 14 and US 20 concurrencies; US 20 resumes in Montana at the park's west entrance
	Park	Cody	49.410	79.518	WYO 291
			51.900	83.525	US 14A east / WYO 120 north – Powell	Western end of WYO 120 concurrency
			54.119	87.096	WYO 120 south – Meeteetse, Thermopolis	Eastern end of WYO 120 concurrency
	Big Horn	​	85.056	136.884	WYO 30 east – Burlington	Western terminus of WYO 30
		​	85.655	137.848	WYO 32 north – Lovell	Southern terminus of WYO 32
		​	99.197	159.642	US 310 north / WYO 789 north – Lovell	Western end of WYO 789 concurrency; southern terminus of US 310
		Greybull	204.05	328.39	US 14 east	Eastern end of US 14 concurrency
		​	199.27	320.69	WYO 36 (Golf Course Road)
		Basin	196.42	316.11	WYO 30
		​	185.52	298.57	WYO 433
		Manderson	184.35	296.68	WYO 31
	Washakie	Worland	0.00	0.00	US 20 east / WYO 789 south / WYO 432 south	Eastern end of US 20 and WYO 789 concurrencies; northern terminus of WYO 432
		Ten Sleep	26.42	42.52	WYO 434
		​	30.04	48.34	WYO 436
		​	33.90	54.56	WYO 435
	Johnson	Buffalo	92.12	148.25	I-25 BL / US 87 Bus. / WYO 196 (Main Street)	Western end of WYO 196 concurrency
			100.00	160.93	I-25 BL / US 87 Bus. / WYO 196 (Main Street)	Eastern end of WYO 196 concurrency
		​	100.61	161.92	I-25 / US 87	I-25 exit 299
		​	2.12	3.41	I-90	I-90 exit 58
	Sheridan	Ucross	17.64	28.39	US 14 west	Western end of US 14 concurrency
		​	54.72	88.06	WYO 341
	Campbell	​	102.07	164.27	WYO 59	Western end of WYO 59 concurrency
		Gillette	114.86	184.85	WYO 50 (Skyline Drive)
			113.10	182.02	WYO 59 (Douglas Highway)	Eastern end of WYO 59 concurrency
			127.57	205.30	I-90 west / WYO 51 ahead	Western end of I-90 concurrency; I-90 exit 128
	Crook	Moorcroft	153.41	246.89	I-90 east	Eastern end of I-90 concurrency; I-90 exit 153
			153.56	247.13	WYO 51
			200.00	321.87	US 14 east	Eastern end of US 14 concurrency
	Weston	Upton	219.83	353.78	WYO 116	Western end of WYO 116 concurrency
			220.13	354.26	WYO 116	Eastern end of WYO 116 concurrency
		Osage	233.29	375.44	WYO 451
		​	245.67	395.37	WYO 450
		Newcastle	247.34	398.06	US 16 Bus. / US 16 Truck
			248.99	400.71	US 16 Bus. / US 16 Truck
			249.82	402.05	US 85
			259.08 0.00	416.95 0.00	Wyoming–South Dakota state line
South Dakota	Custer	Custer	26.46	42.58	US 385 / SD 89	Western end of US 385 and SD 89 concurrencies
			26.96	43.39	US 16A / SD 89	Eastern end of SD 89 concurrency
	Pennington	​	37.49	60.33	SD 87 (Needles Highway)
		​	37.69	60.66	SD 244
		Hill City	40.51	65.19	US 16 Truck / US 385 Truck
			41.06	66.08	US 16 Truck / US 385 Truck
		​	45.00	72.42	US 385	Eastern end of US 385 concurrency
		​	50.60	81.43	US 16A
		​			Rockerville	Interchange; left exits and entrances
		Rapid City	64.19	103.30	US 16 Truck
			69.00	111.04	SD 44 (Omaha Street) to I-190	Eastern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

• U.S. Route 116
• U.S. Route 216

• U.S. Route 16A in South Dakota
• Special routes of U.S. Route 16

• Endpoints of US 16
• Highways and Gas Stations- US Hwy 16 Page
• 1937 South Dakota Transportation Map
• 1930 Minnesota Transportation Map
• 1937 Wisconsin Transportation Map