A special route of the United States Numbered Highway System is a route that branches off a U.S. Highway in order to divert traffic from the main highway. Special routes are distinguished from main routes by, in most cases, the addition of an auxiliary plate that describes what type of route it is, while the main highway carries no such sign. In some locations, a single letter is placed after the route number to denote the special route type in lieu of the auxiliary plate.

There are four main types of special routes — alternate, business, bypass, and temporary; though other route types exist. Alternate routes exist where an additional road is needed to meet traffic demands. They are to be of equal character and quality compared to the main road. Business routes carry traffic through the central business district of a community while the main highway goes around the community. Bypasses serve the opposite purpose of business routes. Truck routes are a subset of bypasses. Temporary routes complete a gap between two segments of main highway that exists because the main highway has not been fully constructed.

A unique type of route in the U.S. Route system uses directional letter suffixes following the route number. These are known as divided U.S. Routes and are generally not considered to be special routes.

The following U.S. Highway special routes have existed: Routes are sorted by position along the main route, from south to north and west to east. Defunct routes are listed in italics.

US 1 – US 101

US 1

Bus. US 1 - Florida City to Homestead, Florida Alt. US 1 - Daytona Beach to St. Augustine, Florida Bus. US 1 - St. Augustine, Florida Alt. US 1 - Jacksonville, Florida Alt. US 1 - Jacksonville, Florida Bus. US 1 - Waycross, Georgia Bus. US 1 - Swainsboro, Georgia Bus. US 1 - Wadley, Georgia Bus. US 1 - Louisville, Georgia Conn. US 1 - Augusta, Georgia to North Augusta, South Carolina Truck US 1 - Aiken, South Carolina Conn. US 1 - Lexington, South Carolina Conn. US 1 - Columbia, South Carolina Truck US 1 - Camden, South Carolina Truck US 1 - Cheraw, South Carolina US 1A - Moore County, North Carolina US 1A - Southern Pines, North Carolina Bus. US 1 - Southern Pines, North Carolina Bus. US 1 - Vass to Cameron, North Carolina US 1A - Sanford, North Carolina Bus. US 1 - Sanford, North Carolina Byp. US 1 - Sanford, North Carolina US 1A - Cary to Raleigh, North Carolina US 1A - Raleigh, North Carolina US 1A - Raleigh, North Carolina Bus. US 1 - Raleigh, North Carolina Byp. US 1 - Raleigh, North Carolina US 1A - Wake Forest to Youngsville, North Carolina US 1A - Franklinton, North Carolina US 1A - Henderson, North Carolina Bus. US 1 - Henderson, North Carolina Byp. US 1 - Henderson, North Carolina Bus. US 1 - Fredericksburg, Virginia Truck US 1 - Alexandria, Virginia Byp. US 1 - Washington, D.C. Alt. US 1 - Washington, D.C. to Hyattsville, Maryland Alt. US 1 - Arbutus to Baltimore Bus. US 1 - Bel Air to Hickory, Maryland Alt. Truck US 1 - West Grove, Pennsylvania Byp. US 1 - Swarthmore to Hunting Park, Pennsylvania Alt. Truck US 1 - Philadelphia Bus. US 1 - Penndel, Pennsylvania Alt. US 1 - Trenton, New Jersey Bus. US 1 - Trenton, New Jersey Byp. US 1 - Trenton, New Jersey Temp. US 1 - Newark to Jersey City, New Jersey Truck US 1 - Newark to Jersey City, New Jersey, via Kearny Bus. US 1 - Jersey City, New Jersey to New York state line at New York City (now designated New Jersey Route 139 and an at-grade portion of Interstate 78) US 1A - Port Chester, New York US 1A - Stamford, Connecticut US 1A - Darien, Connecticut US 1A - Norwalk, Connecticut US 1A - Bridgeport, Connecticut US 1A - Milford, Connecticut US 1A - East Haven, Connecticut US 1A - Branford, Connecticut US 1A - Old Saybrook, Connecticut US 1A - Waterford, Connecticut US 1A - Groton, Connecticut US 1A - Stonington, Connecticut Bus. US 1 - Warwick, Rhode Island US 1A - Norwood, Rhode Island to Massachusetts state line at Attleboro, Massachusetts, via Providence, East Providence, and Pawtucket, Rhode Island Byp. US 1 - Portsmouth, New Hampshire to Kittery, Maine US 1A - York, Maine US 1A - Portland, Maine Bus. US 1 - Newcastle to Damariscotta, Maine US 1A - Rockland, Maine US 1A - Stockton Springs to Ellsworth, Maine, via Bangor Bus. US 1A - Bangor to Brewer, Maine Byp. US 1 - Rockland, Maine US 1A - Milbridge to Harrington, Maine US 1A - Whitneyville to Machias, Maine US 1A - Mars Hill to Presque Isle, Maine US 1A - Mars Hill to Van Buren, Maine Byp. US 1 - Caribou, Maine

US 2

Bus. US 2 - Cashmere, Washington Bus. US 2 - Wenatchee, Washington Bus. US 2 - Williston, North Dakota Bus. US 2 - Minot, North Dakota Byp. US 2 - Minot, North Dakota Bus. US 2 - Grand Forks, North Dakota to East Grand Forks, Minnesota Truck US 2 - Superior, Wisconsin Bus. US 2 - Ironwood, Michigan (used to exist in Hurley, Wisconsin) Bus. US 2 - Montpelier, Vermont Truck US 2 - St. Johnsbury, Vermont Alt. US 2 - Orono to Old Town, Maine Alt. US 2 - Macwahoc Plantation to Houlton, Maine

US 3

Alt. US 3 – Tyngsborough, Massachusetts to Concord, New Hampshire Bus. US 3 – Tyngsborough, Massachusetts to Concord, New Hampshire Byp. US 3 – Concord, New Hampshire Byp. US 3 – Nashua, New Hampshire Bus. US 3 – Belmont to Laconia, New Hampshire (Unsigned)

US 4

Alt. US 4 – Fair Haven to West Rutland, Vermont Bus. US 4 – Rutland, Vermont Alt. US 4 – Andover to Boscawen, New Hampshire Byp. US 4 – Concord, New Hampshire Alt. US 4 – East Northwood to Dover, New Hampshire

US 5

Alt. US 5 (1933–1941) – New Haven to North Haven, Connecticut Alt. US 5 (1941–1966) – New Haven to North Haven, Connecticut Alt. US 5 – New Haven to Meriden, Connecticut Alt. US 5 (1937–1941) – Lamentation Mountain State Park to Tracy, Connecticut Alt. US 5 (1940s–1950s) – Lamentation Mountain State Park to Tracy, Connecticut Alt. US 5 – Berlin, Connecticut Alt. US 5 – East Hartford to East Windsorhill, Connecticut US 5A – Hartford–Windsor, Connecticut city line to Agawam, Massachusetts Byp. US 5 – South Deerfield, Massachusetts Alt. US 5 – St. Johnsbury to St. Johnsbury Center, Vermont Alt. US 5 – Newport, Vermont Alt. US 5 – Derby Line, Vermont

US 6

Bus. US 6 – Ely, Nevada Spur US 6 – Ely, Nevada Temp. US 6 – Colton to Castle Gate, Utah Bus. US 6 – Helper, Utah Bus. US 6 – Price, Utah Bus. US 6 – Cisco, Utah Byp. US 6 – Grand Junction, Colorado Bus. US 6 - Hastings, Nebraska Bus. US 6 – Lincoln, Nebraska City US 6 – Lincoln, Nebraska City US 6 – Des Moines, Iowa City US 6 – Des Moines, Iowa Bus. US 6 – Davenport, Iowa City US 6 – Davenport, Iowa Temp. US 6 – Moline to Joliet, Illinois Bus. US 6 – Lansing, Illinois to Lake Station, Indiana Bus. US 6 – Bremen, Indiana Bus. US 6 – Napoleon, Ohio Alt. US 6 – Sandusky to Huron, Ohio Alt. US 6 – Rocky River to Cleveland, Ohio Alt. US 6 – Cleveland to East Cleveland, Ohio Alt. US 6 – Euclid to Chardon, Ohio Byp. US 6 – Union City, Pennsylvania Bus. US 6 – Warren, Pennsylvania Bus. US 6 – Tunkhannock Township to Tunkhannock, Pennsylvania Bus. US 6 – Scranton to Carbondale Township, Pennsylvania Alt. US 6 – Philipstown, New York Truck US 6 – Woodbury to Highlands, New York US 6A – Newtown to Southbury, Connecticut US 6A – Plymouth to Hartford, Connecticut US 6A – Woodbury to Willimantic, Connecticut US 6A – Coventry to Windham, Connecticut US 6A – Danielson, Connecticut Bus. US 6 – Scituate, Rhode Island Byp. US 6 – Scituate, Rhode Island Alt. US 6 – Johnston to Providence, Rhode Island Byp. US 6 – Johnston, Rhode Island Temp. US 6 – Marion to Wareham, Massachusetts Byp. US 6 – Bourne to Sagamore, Massachusetts Temp. US 6 – South Dennis to East Dennis, Massachusetts Temp. US 6 – Harwich to Brewster, Massachusetts

US 7 Alt. US 7 – Burlington, Vermont

US 8 Bus. US 8 – Rhinelander, Wisconsin

US 9

Truck US 9 – Georgetown, Delaware Bus. US 9 – Five Points to Lewes, Delaware Temp. US 9 – Upper Township to Somers Point, New Jersey Alt. US 9 – South Toms River to Toms River, New Jersey Alt. US 9 – Jersey City, New Jersey to Inwood Hill Park, New York Temp. US 9 – Newark to Jersey City, New Jersey Truck US 9 – Newark to Jersey City, New Jersey Bus. US 9 – Jersey City, New Jersey to New Jersey/New York state line at New York City Alt. US 9W – Newburgh, New York Alt. US 9 – Rouses Point, New York

US 10

Alt. US 10 – Seattle, Washington Alt. US 10 – Seattle, Washington to Missoula, Montana Bus. US 10 – Coeur d'Alene, Idaho Alt. US 10 – Drummond to Opportunity, Montana Byp. US 10 – Butte, Montana Byp. US 10S – Butte, Montana Byp. US 10 – Billings, Montana Bus. US 10 – Valley City, North Dakota Bus. US 10 – Neillsville, Wisconsin Bus. US 10 – Manitowoc, Wisconsin Bus. US 10 – Reed City, Michigan Bus. US 10 – Clare, Michigan Bus. US 10 – Midland, Michigan Bus. US 10 – Flint, Michigan Bus. US 10 – Pontiac, Michigan (replaced by Bus. US 24)

US 11

Bus. US 11 – Meridian, Mississippi Byp. US 11 – Tuscaloosa, Alabama Truck US 11 – Birmingham, Alabama Alt. US 11 – Chattanooga, Tennessee Bus. US 11 – Chattanooga, Tennessee Byp. US 11 – Chattanooga, Tennessee Byp. US 11 – Cleveland, Tennessee Bus. US 11 – Riceville to Athens, Tennessee Bus. US 11E – Greeneville, Tennessee Truck US 11 – Bristol, Virginia Alt. US 11 – Salem to Roanoke, Virginia Bus. US 11 – Lexington, Virginia Byp. US 11 – Lexington, Virginia Bus. US 11 – Staunton, Virginia Truck US 11 – Staunton, Virginia Alt. US 11 – Winchester, Virginia Byp. US 11 – Lemoyne, Pennsylvania Alt. US 11 – Lemoyne, Pennsylvania

US 12

Bus. US 12 – Walla Walla, Washington Bus. US 12 – Missoula, Montana Bus. US 12 – Helena, Montana Byp. US 12 – Helena, Montana Temp. US 12 – Fallon to Ismay, Montana Bus. US 12 – Eau Claire, Wisconsin City US 12 – Eau Claire, Wisconsin Bus. US 12 – Lake Delton to West Baraboo, Wisconsin Bus. US 12 – Sauk City to Prairie du Sac, Wisconsin City US 12 – Madison, Wisconsin Bus. US 12 - Madison, Wisconsin Byp. US 12 - Madison, Wisconsin Bus. US 12 – Fort Atkinson, Wisconsin Bus. US 12 – Whitewater, Wisconsin Temp. US 12 – Big Foot to Crystal Lake, Illinois Bus. US 12 – Des Plaines to Chicago City US 12 – Des Plaines to Chicago, Illinois Toll US 12 – Chicago, Illinois to Hammond, Indiana Bus. US 12 – Niles, Michigan Alt. US 12 – Kalamazoo, Michigan Bus. US 12 – Kalamazoo, Michigan Alt. US 12 – Battle Creek to Springfield, Michigan Bus. US 12 – Battle Creek, Michigan Bus. US 12 – Marshall, Michigan Bus. US 12 – Albion, Michigan Bus. US 12 – Jackson, Michigan Bus. US 12 – Ypsilanti, Michigan

US 13

Alt. US 13 – Bethel to Williamston, North Carolina Bus. US 13 – Bethel, North Carolina US 13A – Windsor, North Carolina Bus. US 13 – Windsor, North Carolina Bus. US 13 – Suffolk, Virginia Spur US 13 – Norfolk, Virginia Bus. US 13 – Cape Junction to Cheriton, Virginia Byp. US 13 – Cheriton, Virginia Bus. US 13 – Eastville, Virginia Byp. US 13 – Eastville, Virginia Bus. US 13 – Exmore, Virginia Byp. US 13 – Exmore, Virginia Bus. US 13 – Onley to Accomac, Virginia Byp. US 13 – Tasley, Virginia Byp. US 13 – Accomac, Virginia Bus. US 13 – Pocomoke City, Maryland Bus. US 13 – Fruitland to Salisbury, Maryland Alt. US 13 – Delmar to Seaford, Delaware Bus. US 13 – Bridgeville, Delaware Alt. US 13 – Bridgeville, Delaware Alt. US 13 – Woodside to Camden, Delaware Alt. US 13 – Rodney Village to Dover, Delaware Bus. US 13 – Wilmington, Delaware Alt. US 13 – Wilmington to Claymont, Delaware Byp. US 13 – Claymont, Delaware to Chester, Pennsylvania Bus. US 13 - Trainer to Chester, Pennsylvania Byp. US 13 – Chester to Collingdale, Pennsylvania Byp. US 13 – Darby to Hunting Park, Pennsylvania Alt. Truck US 13 – Bensalem Township, Pennsylvania

US 14

Alt. US 14 – Cody to Burgess Junction, Wyoming Bus. US 14 – Sheridan, Wyoming