U.S. Highway 1A (US 1A) is a 9.0-mile (14.5 km) alternate route of US 1 through the towns of Wake Forest and Youngsville.

While serving the downtown areas of both towns, the highway bypasses the primary commercial district of each.

A two-lane urban highway, it follows the old alignment through the downtown area, via Main Street.

It stayed with Post Road through Pawtuxet Village, then traveled north into Cranston on Broad Street to rejoin the current alignment at Norwood Avenue.

At this point, it makes a 90-degree turn onto Commercial Street, which it will follow through the entire waterfront area, passing such landmarks as Becky's Diner and the U.S. Customs Service Portland office.

U.S. Route 1A (US 1A) in Rockland bypasses the downtown area and begins at the intersection of Camden and Maverick streets.

It then takes a 90-degree turn at a flashing yellow blinker light to turn left (south) onto Birch Street where it meets North Main Street (which was the former alignment of SR 17) at a traffic light.

US 1A then continues along Broadway, passing Oceanside High School as it continues south through the residential heart of Rockland, and encounters additional traffic lights at Rankin and Limerock streets, until its end at a traffic light at Park Street where it rejoins US 1.

The route is 54.0 miles (86.9 km) long and runs from Stockton Springs to Ellsworth.

US 1A enters Bangor from the southwest by following the west bank of the Penobscot River through the towns of Winterport and Hampden.

US 1A crosses the Joshua Chamberlain Bridge from downtown Bangor into the city of Brewer and continues southeast through Holden and Dedham to Ellsworth.

It then crosses the Narraguagus River and continues in a northeasterly direction whereas US 1 takes a route that is north-northwest to meet Cherryfield before turning back east while US 1A takes the more direct (and southern) route closer to the coast to rejoin its parent just east of Harrington.

U.S. Route 1A (US 1A) runs 8.1 miles (13.0 km) between Jonesboro and Machias via the village of Whitneyville.

U.S. Route 1A (US 1A) in Aroostook County runs 49.8 miles (80.1 km), from Mars Hill to Van Buren.

The section north of Fort Fairfield to Van Buren was once SR 165 but is no longer a numbered highway in Maine.

U.S. Highway 1A (US 1A) was established around 1957, replacing the old mainline US 1 through Southern Pines, North Carolina, via May Street.

[13] U.S. Highway 1A (US 1A) was established around 1957, replacing the old mainline US 1 through downtown Sanford, North Carolina, via Carthage Street and Hawkins Avenue.

[13] U.S. Highway 1A (US 1A) may have appeared in 1933 as a second route between Cary and Raleigh, North Carolina; it was cosigned with US 70 on Western Boulevard.

[13] The second U.S. Highway 1A (US 1A) in Raleigh, North Carolina, was established in 1948 as a route switch with mainline US 1 onto Wake Forest Boulevard.

[13] U.S. Highway 1A (US 1A) was established around 1957, replacing the old mainline US 1 through Gill and downtown Henderson, North Carolina, via Raleigh Road and Garnett Street.

After the redevelopment, the Main Street portion of US 1 was routed onto the newly created Tresser Boulevard and its accompanying bridge crossing the river.

U.S. Route 1A (US 1A) in Old Saybrook, Connecticut, was designated on the current US 1 alignment on Boston Post Road.

US 1 originally went to the town center using Old Boston Post Road then Main Street (now part of Route 154).