Wyoming Highway 274

U.S. Route 20 or U.S. Highway 20 (US 20) is an east–west United States Numbered Highway that stretches from the Pacific Northwest east to New England. The "0" in its route number indicates that US 20 is a major coast-to-coast route. Spanning , it is the longest road in the United States, and, in the east, the route is roughly parallel to that of the newer Interstate 90 (I-90), which is the longest Interstate Highway in the U.S. There is a discontinuity in the official designation of US 20 through Yellowstone National Park, with unnumbered roads used to traverse the park.

US 20 and US 30 break the general U.S. Route numbering rules in Oregon, since US 30 actually starts north of US 20 in Astoria, and runs parallel to the north throughout the state (the Columbia River and Interstate 84). The two run concurrently and continue in the correct positioning near Caldwell, Idaho. This is because US 20 was not a planned coast-to-coast route while US 30 was. US 20 originally ended at the eastern entrance of Yellowstone Park; it was extended in 1940.

The highway's eastern terminus is in Boston, Massachusetts, at Kenmore Square, where it meets Massachusetts Route 2. Its western terminus is in Newport, Oregon, at an intersection with US 101, within a mile of the Pacific Ocean.

Route description

Oregon

US 20 begins at an intersection with US 101 in Newport, Oregon, and runs generally eastward towards Idaho. On the way it goes over the Central Oregon Coast Range, through several Willamette Valley cities including Corvallis and Albany, climbs the Cascade Mountains over Santiam Pass, goes through Bend, and traverses the Oregon High Desert after passing through Burns. It eventually overlaps US 26 in Vale, and the two highways continue concurrently to the Idaho border.

Idaho

US 20 crosses into Idaho from Oregon northwest of Parma. It runs concurrently with US 26 and joins US 95 through Parma. US 20/US 26 leaves US 95 southeast of Parma and runs to Caldwell where US 20/US 26 joins with I-84 and US 30 for a short time. These four highways parallel each other (on two roadways) to Boise where US 20/US 26 runs through downtown before joining with I-84 and US 30 again to Mountain Home, where it departs at exit 95 to head east, past Rattlesnake Station, Anderson Ranch Dam road, and cresting at Cat Creek summit at above mean sea level. It continues into and across Camas County through Fairfield to Timmerman Junction, the intersection in Blaine County with State Highway 75, the route to Sun Valley, Galena Summit, and Stanley. US 20 continues east through Picabo and Carey, joined with US 26 and US 93, to Craters of the Moon and Arco, where US 93 splits off and turns north-northwest to climb the Big Lost River valley. US 20/US 26 continues on through the Idaho National Laboratory, where the highways split just west of Atomic City; US 26 heads to Blackfoot and US 20 to Idaho Falls, where it turns north-northeast to pass near Rexburg as a freeway. US 20 then climbs through the communities of St. Anthony, Ashton, and Island Park, and crosses the Continental Divide at Targhee Pass at , entering Montana west of West Yellowstone.

Montana

In the state of Montana, US 20 runs for less than . It runs from the Idaho state line to West Yellowstone, Montana, the western entrance to Yellowstone National Park. US 20 is known as the Targhee Pass Highway in Montana.

While US 20 and other U.S. Routes are officially discontinuous through the park, some commercially produced maps show these highways running inside Yellowstone National Park itself along its unnumbered roads and across the Montana–Wyoming state line.

Wyoming

In the state of Wyoming, the eastern segment of US 20 starts at the eastern entrance to Yellowstone National Park along with the western termini of US 14 and US 16. These three routes run east to Greybull, where US 14 continues east and US 16/US 20 turns south; at Worland, US 16 turns east while US 20 continues south, passing through Wind River Canyon south of Thermopolis. US 20 joins US 26 in Shoshoni, where it turns east, and they continue all the way through Casper. From Casper, the two highways parallel I-25 and US 87 for 26 miles, until all four link up together just southeast of Glenrock. These four routes stay combined to Orin, where US 20 turns east from I-25, at the western end of US 18. US 18 and US 20 are concurrent from Orin to Lusk, where US 18 turns north and US 20 continues east into Nebraska.

Nebraska

Within Nebraska, US 20 is a state highway that begins on the Wyoming–Nebraska state line west of Harrison near the Niobrara River and runs to the Nebraska– Iowa state line in South Sioux City. Throughout its length the route passes through a diverse range of landscapes including bluffs and escarpments in the Northwest Panhandle, the Nebraska Sandhills in the northern part of the state, and rolling hills and plains as the highway approaches the Missouri River valley south of Sioux City, Iowa. Throughout its length, US 20 is a two-lane highway with the exception of the easternmost which is four-lane divided highway, the last of which is concurrent with Interstate 129.

Iowa

US 20 enters Iowa at Sioux City via the Missouri River crossing with I-129 and US 75. After skirting the southeast side of Sioux City as a freeway with US 75, US 20 continues east as an expressway to Moville. From Moville through north of Early at the junction with U.S. Route 71 and Iowa Highway 471, US 20 was reconstructed from a rural two-lane highway to a four-lane road. This segment re-opened October 19, 2018 and made it so that US 20 is a continuous four-lane highway for its entire length in Iowa. It passes to the north of Sac City, where it has another interchange with the realigned U.S. Route 71, then passes to the south of Fort Dodge and Webster City before intersecting I-35 near Williams.

A new segment of freeway between US 65 south of Iowa Falls and Iowa Highway 14 opened in 2003 creating a continuous four-lane route from Moorland to Dubuque. The new segment shaved off US 20's length in Iowa. In the Waterloo/ Cedar Falls area, the segment of US 20 overlapped by the Avenue of the Saints, which is also designated as Iowa Highway 27. US 20 passes Independence, Manchester, and Dyersville before reaching Dubuque. At Dubuque, US 20 crosses into Illinois over the Julien Dubuque Bridge.

Illinois

In the state of Illinois, US 20 begins in East Dubuque, following southeastward along the Mississippi River, and continues into the very hilly Driftless Area of northwest Illinois through Galena and Elizabeth. The highway then transitions eastward from the Driftless Area to the Interior Plains near Stockton. The road continues as a bypass north of Freeport, and then runs as a freeway along the southern fringe of Rockford. From Rockford to Chicago, Illinois, US 20 is a mixture of four-lane expressway, four-lane limited access freeway, and winding two-lane surface road. It is signed as "General U.S. Grant Highway" after Ulysses S. Grant. U.S. 20 runs through the south side of Chicago as 95th Street. US 20 exits Illinois along with US 12 and US 41 as Indianapolis Boulevard south of the Chicago Skyway.

Indiana

In the state of Indiana, US 20 enters from the west beneath the Chicago Skyway with US 12 and US 41. US 20 passes through heavily industrialized northwestern Indiana and is the main east–west artery through Gary. It then parallels US 12 to just west of Michigan City before running due east through New Carlisle to South Bend. US 20 travels around South Bend and Elkhart on the St. Joseph Valley Parkway, a four-lane limited access freeway, then returns to surface road east of Elkhart. US 20 then passes through LaGrange

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