U.S. Route 20 in Wyoming

US 14, US 16, and US 20 at the East Entrance of Yellowstone Park

Google Maps and other mapmakers may show US 20 and other U.S. Highways going through Yellowstone National Park;[2] however, they are officially discontinuous and unsigned inside the park.[3]

Unofficially, Google Maps marks the start of the western part of US 20, along with US 191 and US 287, at the state line near West Yellowstone, Montana. The road parallels the Madison River until a junction with US 89.[4] The three routes then turn south along US 89 (Grand Loop Road), paralleling the Firehole River. Past Old Faithful, the four routes curve east before reaching the West Thumb of Yellowstone Lake. While the rest of the routes turn south, US 20 travels northeast along the lake. US 20 even leaves the Grand Loop Road at an intersection midway along the lake. This intersection also marks the western "terminuses" of US 14 and US 16. US 20 travels through for 65.8 miles (105.9 km) by the time it exits the park.[5]

US 20, US 26, and US 87 exiting I-25 in Casper

The eastern section of US 20 begins at the east entrance of Yellowstone National Park. US 20, along with US 14 and US 16, then meanders east along the Shoshone River, heading toward Wapiti, Buffalo Bill Reservoir, and Cody. US 14A begins at Cody and continues to follow the river, while the three head straight to Greybull. Before Greybull, however, Wyoming Highway 789 (WYO 789) joins the concurrency. At Greybull, US 14 leaves the concurrency. At this point, the concurrency parallels the Bighorn River. In Worland, US 16 turns east and leaves the concurrency. South of the Boysen Dam, the road runs along the eastern front of the Boysen Reservoir. In Shoshoni, US 20 turns east along US 26, while WYO 789 turns west along the same route.[6]

As US 20 and US 26 head toward Casper, the two routes travel along a limited-access road before traveling east along I-25 and US 87. US 20, US 26, and US 87 exit onto Beverly Street (exit 186) and travel east along Yellowstone Highway. Before reaching Glenrock, the three U.S. Highways are sandwiched between the North Platte River to the north and I-25 to the south. The three routes rejoins the interstate after Glenrock. US 20 leaves the freeway at Orin; this interchange is also where US 18 begins eastward. US 87 briefly joins the concurrency before US 20 turns east away from US 18/US 85. After passing through Van Tassell, US 20 crosses the Nebraska state line.[6]