U.S. Route 1 in Massachusetts

Most of US 1 consists of two former turnpike roads — the Norfolk and Bristol Turnpike and the Newburyport Turnpike. The older roads that these turnpikes were meant to bypass are now mostly Route 1A.

In the early 1930s, Route C1 was designated as an alternate route of US 1 through downtown Boston. The "C" indicated a city route. The C designation was apparently distinct to the Boston area. Route C1 ran along Brookline Avenue, Beacon Street, Embankment Road (modern Route 28), Charles Street, Lowell Street, Merrimac Street, and Cross Street to the west end of the Sumner Tunnel. In East Boston, it went via Porter Street to Chelsea Street then shifted to the William McClellan Highway (modern Route 1A). As Storrow Drive and the Central Artery opened in the 1950s, Route C1 was rerouted to follow portions of these highways. The Route C1 designation was removed in 1971, with US 1 taking over most of the alignment south of the Charles River, and Route 1A taking over most of the alignment north of the river. US 1 was later moved onto the Southeast Expressway leaving most of the former alignment of C1 south of the river as having no number.

For a period of time during the 1950s, a segment of US 1 in Massachusetts and New Hampshire was routed onto what later became Interstate 95 (I-95). Roadway that had been US 1 was designated as Route 17 from Danvers to Salisbury,[4] and New Hampshire Route 17 (NH 17) for a short distance in Seabrook.[5] Once the I-95 designation was adopted, Route 17 and NH 17 were restored to being US 1.

Causeway (center) for the unbuilt section of the Northeast Expressway across Saugus Marsh

The Northeast Expressway was planned to extend north, as part of Interstate 95, from Saugus, through Lynn, Lynnfield and Peabody. The highway would bisect the Saugus Marsh and the Lynn Woods Reservation. The highway would then connect with the present junction of I-95 and Route 128 in Peabody. The Northeast Expressway was planned to carry the I-95 designation from Charlestown to Peabody. The first section of the expressway built was the Tobin Bridge over the Mystic River, which opened in 1950. In various stages, the Chelsea and Revere portions opened from 1956 to 1958. The highway carried the I-95 designation from 1955 (in its planning stages) to 1973. It was among the canceled highways affected by Gov. Francis Sargent's February 1970 moratorium on expressway construction within Route 128. US 1 replaced I-95 on the Northeast Expressway, in the 1970s after I-95 joined Route 128 from Westwood to Peabody around Boston.[6]

In the late 1980s, at the request of the Metropolitan District Commission (now the DCR) in an attempt to reduce the incidence of overheight vehicles finding their way onto Storrow Drive,[7] US 1 was moved onto I-93 south of and through Boston, leaving the old route—VFW Parkway, Jamaicaway, Riverway, and Storrow Drive through Dedham, Chestnut Hill, West Roxbury, Jamaica Plain and central Boston—without a number. There are still some street signs incorrectly indicating the former alignment as US 1, and many local residents still refer to parts of VFW Parkway and Jamaicaway as "Route 1", as if it still runs along its old trajectory.

1955 Yellow Book plan for the Boston area showing the Northeast Expressway path and paths of other proposed interstate highways within Route 128.

In the early 2010s, the Massachusetts Department of Transportation (MassDOT) proposed a $137 million project to widen the existing 2.4-mile (3.9 km) four-lane highway section to six lanes, from north of Route 99 in Saugus to south of Route 60 in Revere. The proposal consisted of adding a 12-foot (3.7 m) travel lane and 10-foot (3.0 m) shoulder in each direction. Work would also include reconstruction of the Copeland Circle interchange by eliminating the existing rotary, and demolition of the existing 1957 bridges from the never-built highway extension. The Lynn Street/Salem Street interchange in Malden, and the Route 99 interchange in Saugus, were slated to be reconstructed. Major rock blasting would be required for the project due to a massive ledge next to the highway, and seven bridges would be replaced and three others upgraded to handle the new lanes. In 2012, $10 million was added to the state budget with the intent to be used for design costs and pulling permits for Route 1.[8] The project was expected to begin in 2012, but no further movement by the state has been implemented. Since then, town officials have made the push to ask MassDOT to revisit the project and begin development.[9]