Since it was pieced together from other routes, US 6 does not serve a major transcontinental corridor, as other highways like U.S. Route 40 do. George R. Stewart, author of U.S. 40: Cross Section of the United States of America, initially considered US 6, but realized that "Route 6 runs uncertainly from nowhere to nowhere, scarcely to be followed from one end to the other, except by some devoted eccentric". In the famous "beat" novel On the Road by Jack Kerouac, protagonist Sal Paradise actually considers hitchhiking on US 6 to Nevada, but is told by a driver that "there's no traffic passes through 6" and that he'd be better off going via Pittsburgh (the Pennsylvania Turnpike). |- |CA |41 |66 |- |NV |305 |491 |- |UT |373 |600 |- |CO |467 |752 |- |NE |373 |600 |- |IA |320 |515 |- |IL |172 |277 |- |IN |149 |240 |- |OH |259 |417 |- |PA |394 |634 |- |NY |78 |126 |- |CT |116 |187 |- |RI |25 |40 |- |MA |118 |190 |- |Total |3205 |5158 |}
Currently, US 6 begins at U.S. Route 395 just north of Bishop and heads north between farms and ranches in the Chalfant Valley, California at the base of the 9,000-foot (2,700 m) western escarpment of the White Mountains. After about 30 miles (50 km.) Benton is reached which has a cafe and gas station. California State Route 120 begins here, heading west past Mono Lake through Lee Vining, California, over Tioga Pass and through Yosemite National Park to the San Joaquin Valley. US 6 continues north to the Nevada state line.
From the pass, U.S. Route 6 descends into barren shadscale desert, passing Columbus Salt Marsh on the left, then merging with U.S. Route 95 from Coaldale Junction to Tonopah. Nevada Test and Training Range begins about 15 miles (25 km.) southeast of Tonopah.
Just east of Tonopah, U.S. Route 6 continues east across a series of desert mountain ranges and valleys, including the Monitor Range. At Warm Springs, Nevada Nevada State Route 375, also known as the "Extraterrestrial Highway" departs to the southeast and Route 6 assumes a northeasterly alignment across the Reveille, Pancake, Grant and White Pine Ranges. Rainfall increases eastward, so valleys become less barren and peaks over 11,500' (3,500 m.) add scenic interest.
Ely, Nevada is the largest town on Route 6 in Nevada. U.S. Route 50 joins Route 6 at Ely. East of Ely, Routes 6/50 cross the Schell Creek Range, known for verdant forests and meadows, and for a large deer and elk population. The highway descends to the Snake Valley, then crosses the Snake Range at Sacramento Pass north of Nevada's second-highest Wheeler Peak where a branch road accesses Great Basin National Park. Beyond the pass, Route 6 passes just north of Baker, Nevada a Mormon farming community and reaches the Utah state line.
U.S. 6 enters Iowa at Council Bluffs across the Missouri River from Omaha. It heads due east until Lewis, where it turns sharply north-northeast to Atlantic. There, it overlaps with U.S. Route 71 north until Interstate 80. It overlaps with I-80 between U.S. 71 and U.S. 169 at De Soto. It goes north with U.S. 169 to Adel, then turns east to go through Des Moines. At Altoona, U.S. 6 rejoins I-80. It continues east with I-80 until Newton, where it splits north from I-80 to run parallel. U.S. 6 passes through Grinnell and Marengo before arriving in Iowa City where it again crosses 80. At West Liberty, it proceeds due east until Wilton where it turns north to concurrency again with 80. Arriving in Davenport, it becomes Kimberly Road until Interstate 74 with which it runs across the Mississippi River on the I-74 Bridge into Moline, Illinois.
Alternate 6 exists to provide a route for truck traffic, as commercial vehicles are prohibited on Clifton Blvd.
For the remainder of its routing in Pennsylvania, US 6 runs roughly parallel to the New York-Pennsylvania border. Along the way, US 6 is concurrent with U.S. Route 62 for a short distance near Warren. U.S. Route 11 joins US 6 from the north in Factoryville. They run concurrently to North Scranton where US 11 continues south and US 6 east. At Milford, US 6 meets U.S. Route 209. The two routes embark to the northeast, crossing the Delaware River from Matamoras to Port Jervis.
The portion of US 6 in New York is located primarily in Orange County, with lengthy stretches in Putnam County and Westchester County and a small segment in Rockland County. The route enters the state along with US 209 in Port Jervis. The two routes split just north of town, with US 209 taking a more northerly routing to access Kingston. US 6, in contrast, runs primarily east-west through New York.
A section of US 6 runs concurrent with New York State Route 17 (the Quickway) between Goshen and Harriman. At Harriman, NY 17 becomes an at-grade road and heads south while US 6 remains a limited-access highway as it heads east into Harriman State Park. Near the east side of the park, US 6 intersects the Palisades Interstate Parkway and runs concurrent to the road to the Bear Mountain Bridge, where US 6 is joined by U.S. Route 202 as it crosses the Hudson River.
On the other side of the river, US 6 and US 202 run along the Hudson to Peekskill, where the two routes split, allowing US 6 to continue to the northeast into Putnam County. In Brewster, US 6 meets US 202 once again. The routes become intertwined once more, running concurrent with one another into Connecticut.
US 6 covers approximately in Rhode Island from Foster (western border with Killingly, CT) to East Providence (eastern border with Seekonk, MA). In and around Providence, US 6 overlaps with RI 10 as well as US 1A and US 44 and interstate highways 95 and 195.
The first interstate numbering along the path of US 6 was Route 3 (NE-3) of the New England road marking system, designated in 1922. This route connected Provincetown with the Connecticut-New York border via Providence, Hartford, and Danbury. In late 1925, the Joint Board on Interstate Highways approved the preliminary plan for U.S. Highways. US 6 was restricted to New England and southeastern New York, with its vague description matching the existing Route 3 to Danbury, Connecticut, and heading west from there to U.S. Route 7 at Brewster, New York. By the time the final plan was approved in late 1926, a second section had been added, from the New York-Pennsylvania border at Port Jervis, New York west to U.S. Route 120 in Kane, Pennsylvania. This did not last long, for the April 1927 route log shows the eastern segment running only to the border of New York, short of Brewster, while the western segment was extended in both directions - east to Kingston, New York, and west to Erie, Pennsylvania (the latter replacing part of US 120). The western segment was also swapped with U.S. Route 106 between Carbondale and Tunkhannock, Pennsylvania, taking US 6 through Scranton. The gap through New York was eliminated in 1928 with a new alignment across the state, crossing the Hudson River on the Bear Mountain Bridge; the old route between Kingston and Port Jervis became the first U.S. Route 6N.
While US 6 replaced the general corridor of Route 3 in New England, some portions used different alignments. One of these was on Cape Cod, where Route 3 had used a southerly alignment that is now Route 28. Instead, US 6 followed the more direct route between Buzzards Bay and Orleans that had been the southern extremity of Route 6, and now known as Route 6A. Further west, in Connecticut, US 6 ran via South Coventry, while Route 3 had served Andover; the old route became U.S. Route 6A. US 6 is now on the old Route 3, while the South Coventry route now carries Route 31. A different alignment was also chosen for US 6 between Plainville and Woodbury; Route 3 ran via Milldale and Waterbury, and became parts of Route 14 and Route 10 in the 1932 renumbering. Here US 6 mostly remains on its original routing, with the main difference being between Hartford and Terryville, where US 6 followed the present Route 4, Route 10, and Route 72. The final difference was from Danbury west to the New York state line; here US 6 ran straight west, while Route 3 had left the Danbury area to the south, curving to the southwest through Ridgefield to the border. Part of this became U.S. Route 7, while the rest became Route 35 in 1932.
In New York, US 6 replaced all of Route 37 - known as the "Bridge Route" - over the Bear Mountain Bridge, overlapped part of Route 17, and was assigned to an unnumbered road from Middletown west to Port Jervis. The original route, which soon became US 6N, replaced Route 50, and is now part of U.S. Route 209. The part of US 6 in Pennsylvania replaced Route 7, also known as the Roosevelt Highway, an auto trail. The Roosevelt Highway Association extended the name east with US 6 to Cape Cod by 1930.
Most of US 32 and all of US 38 became a western extension of US 6 on June 8, 1931, and the Roosevelt Highway name followed. To connect western Pennsylvania to central Indiana, relatively minor roads were used, except west of Joliet, where it used a part of the old Detroit-Lincoln-Denver Highway. The short stub to Erie formed at the old west end became U.S. Route 6N, and US 32 remained in Illinois, running independently from Chicago to Princeton and overlapping US 6 to Davenport, Iowa. US 32 has since been absorbed into U.S. Route 34.
The Roosevelt Highway Association continued to push for an extension, and in December 1936 the American Association of State Highway Officials made US 6 (and thus the Roosevelt Highway) a transcontinental route from Cape Cod, Massachusetts to Long Beach, California. It took a new route from Wiggins, Colorado, southwest to Denver (the old route to Greeley became an extended U.S. Route 34) and west over the Rocky Mountains to Leadville, overlapping U.S. Route 24 to Grand Junction and U.S. Route 50 to Spanish Fork, Utah. From Spanish Fork to Ely, Nevada, it followed a roadway that had yet to be improved in areas; the rest of the route, from Ely to Southern California, followed the old Midland Trail, running almost north-south in California. The unimproved segment from Ely east to Delta, Utah, about 160 miles (260 km) long, was, according to Business Week, "nothing but a wagon trail-rutted, filled with dust...one of the worst chunks of federal [sic] road in the country." Paving was completed in September 1952, with a two-day celebration in Delta marking the occasion.
Major William L. Anderson, Jr. of the U.S. Army recommended that US 6 be designated the Grand Army of the Republic Highway, honoring the Union soldiers in the Civil War. The Sons of Union Veterans of the Civil War began pushing for the name in April 1934. Massachusetts, the first state to apply the name, passed a law to do so on February 2, 1937; it was not until at least 1948 that all states had agreed. The highway was formally dedicated at the Long Beach end on May 3, 1953, though the Roosevelt Highway Association continued to exist at least through the 1960s.
Starting in the spring of 1983 U.S. 6 was a discontinuous route for almost one year, due to a massive landslide that destroyed the town of Thistle, Utah. The highway was rebuilt by blasting a path higher up the canyon wall. The landslide remains the most costly in the history of the United States.