U.S. Route 20 (Idaho)
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| U.S. Route 20 (Idaho) | |
|---|---|
.png) | |
| State | ID |
| Type | US |
| Route | 20 |
| Length mi | ??? |
| Direction a | West |
| Terminus a | Oregon |
| Direction b | East |
| Terminus b | Wyoming |
U.S. Route 20 (Idaho)
U.S. Route 20 (Idaho) is the Idaho segment of U.S. Route 20, a transcontinental highway that connects the Pacific Ocean at Astoria, Oregon with Boston on the Atlantic Ocean. The corridor traverses western, central, and eastern Idaho, linking communities such as Ontario's border area, Boise, Mountain Home, Idaho Falls, and the Yellowstone National Park gateway, and provides connections to major routes including I‑84 and Interstate 15.
Route description
The western approach enters Idaho near Ontario and immediately provides access to the Snake River valley, passing near Marsing, Nampa, and Meridian, where it intersects I‑84 and serves as a primary arterial into the Boise Metropolitan Area. From Boise, the route proceeds eastward, skirting the Boise River, crossing the Lucky Peak Reservoir corridor and traversing Eagle and Star, before continuing toward Mountain Home and the Snake River Plain. East of Mountain Home the highway crosses rangeland and agricultural areas toward Hammett and Glenns Ferry, providing access to the Oregon Trail corridor and the Fort Boise. The highway then aligns with the route to Blackfoot and Idaho Falls, where it intersects I‑15 and serves regional traffic bound for the Snake River Plain irrigated farmlands. Continuing east, the highway follows mountain valleys and high desert toward Rigby, St. Anthony, and the approaches to West Yellowstone, entering the vicinity of Yellowstone National Park and crossing into Wyoming near historic Monida Pass corridors.
History
The corridor traces alignments used by 19th‑century emigrant trails, including sections of the Oregon Trail and wagon roads that supported Fort Hall and Fort Boise traffic. Early 20th‑century transcontinental auto routes used portions of this alignment prior to federal numbering; the designation as part of U.S. Route 20 was established with the creation of the United States Numbered Highway System in 1926. Over decades the route was realigned to bypass downtowns such as Boise and Idaho Falls, and to accommodate construction of I‑84 and I‑15. Notable projects included grade separations near Nampa and the reconstruction of river crossings near Lucky Peak State Park and irrigation structures associated with the Minidoka Project.
Major intersections
Major junctions include the western border crossing near Ontario connecting with US‑95 corridors, an interchange with I‑84 near Nampa and Meridian, urban intersections in Boise providing access to SH‑55 and SH‑21, the Mountain Home area junction with I‑84 and SH‑51 corridors, the crossing of the Snake River near Glenns Ferry, an interchange at Blackfoot with US‑26 and access to Idaho National Laboratory corridors, the I‑15 interchange at Idaho Falls connecting to US‑26 and regional parkway links, and eastern intersections serving West Yellowstone and the Yellowstone National Park entrance road network.
Related highways and concurrencies
Throughout Idaho, the route shares pavement or aligns closely with several numbered highways. Concurrencies occur with US‑26 across portions of the Snake River Plain and through Idaho Falls, and alignments with US‑93 and US‑191 appear on approach segments toward eastern Idaho destinations. Connections to the Interstate Highway System include interchanges with I‑84 near Meridian and Mountain Home and with I‑15 at Idaho Falls, providing through routes to Salt Lake City, Ogden, Pocatello, and Butte. The corridor also intersects multiple State Highways such as SH‑55, SH‑21, and SH‑33.
Special routes and business loops
Several business routes and bypass segments serve local downtowns: business loops penetrate Nampa and Idaho Falls central districts, maintaining continuity with historic downtown commercial strips and providing connections to municipal facilities. Alternate alignments historically provided routes into Boise proper prior to construction of beltway and freeway segments; some former alignments are now designated as state or county highways serving communities including Mountain Home Air Force Base approach roads and industrial access to Twin Falls area agricultural distribution centers.
Future developments and improvements
Planned projects focus on capacity and safety improvements coordinated by the Idaho Transportation Department and regional planning organizations such as the Treasure Valley Regional Planning Organization and the Eastern Idaho Regional Airport area authorities. Proposed works include interchange upgrades near Nampa and Meridian, widening and shoulder improvements across the Snake River Plain, bridge rehabilitation at Lucky Peak and Snake River crossings, and multimodal access enhancements to Boise transit corridors and Yellowstone National Park east‑gateway facilities. Funding sources cited in planning documents include federal programs administered with partners such as the Federal Highway Administration and regional economic development agencies tied to tourism and freight corridors.
Category:U.S. Highways in Idaho Category:Transportation in Ada County, Idaho Category:Transportation in Bonneville County, Idaho