Route 3A is a 97-mile-long (156 km) state highway in eastern Massachusetts, which parallels Route 3 and U.S. Route 3 from Cedarville in southern Plymouth to Tyngsborough at the New Hampshire state line.

Quick Facts Route 3A, Route information ...

Route 3A
Route 3A highlighted in red
Route information
Maintained by MassDOT
Length	97 mi[1] (156 km)
Existed	1926–present
Southern section
Length	53.392 mi[1] (85.926 km)
South end	Route 3 in Plymouth
Major intersections	US 44 in Plymouth Route 53 in Kingston Route 53 in Quincy
North end	I-93 / US 1 / Route 3 / Route 203 in Boston
Northern section
Length	22.5043 mi[1] (36.2172 km)
South end	I-95 / US 3 / Route 128 in Burlington
Major intersections	Lowell Connector in Lowell Route 110 in Lowell Route 113 in Tyngsborough
North end	NH 3A in Hudson, NH
Location
Country	United States
State	Massachusetts
Counties	Plymouth, Norfolk, Suffolk, Middlesex
Highway system
Massachusetts State Highway System Interstate US State
← Route 3 → Route 3B
← Route 6 N.E. → Route 7

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Route 3A has two major posted segments, separated by a lengthy concurrency with Route 3 and US 3. Its southern portion parallels Route 3 from Cedarville in southern Plymouth to Neponset in the Dorchester area of Boston. Towns and cities that Route 3A traverse along its path include Plymouth, Kingston, Duxbury, Marshfield, Scituate, Cohasset, Hingham, Weymouth and Quincy.

North of Neponset, Route 3A runs, unsigned, concurrently with Route 3 and U.S. Route 3 to Burlington, before separating again (MassDOT counts the mileage along MA 3 between the two sections as part of MA 3A mileage).

The northern portion of Route 3A parallels U.S. Route 3 in northwestern Middlesex County. It stretches from Interstate 95 (Route 128) in Burlington to the New Hampshire state line, where it continues as Route 3A.

From 1922 to 1926, Route 3A between Kingston and Quincy was New England Interstate Route 6A. In 1926, when New England Interstate Route 6 became Route 3, Route 6A became Route 3A.

In the 1930s Route 3A's route was shifted onto new alignments built to reduce traffic problems in several communities through which the highway traversed. This included a bypass of Hingham Square along Broad Cove Road and Otis Street along Hingham Harbor replacing the original route that took it down Lincoln Street to downtown Hingham then along North Street to Summer Street. Chief Justice Cushing Highway was built around the same time and Route 3A was put on this highway from south of the Hingham Harbor rotary through Cohasset to Scituate. This replaced a routing along long-existing roadways such as Country Way in Scituate, South and North Main Streets in Cohasset and East Street to Summer Street in Hingham. Along East Street from Hull Street to Summer, Route 3A shared the highway with Route 128 in the late 1920s and early 1930s.

In the 1950s and early 1960s Route 3A was extended to take over the original path of Route 3 south of Kingston to Plymouth and north of downtown Quincy to Neponset when Route 3 assumed its current freeway route. In between those locations, old Route 3 was designated Route 53. The section of old Route 3 from Cedarville south to the Sagamore Rotary near the Cape Cod Canal in Bourne is unnumbered.

Much of Route 3A is sometimes referred to as the "Cape Way" due to its history as the only major road to Cape Cod from Boston prior to the opening of Route 3. The "Cape Way" name is reflected in numerous business names along 3A's length.

The section of Route 3A south of the intersection with Route 113 in Tyngsborough (all but the northern few miles of the route) was formerly U.S. Route 3, prior to the construction of the Northwest Expressway, a freeway connection from I-95 in Burlington to the Everett Turnpike in Nashua, New Hampshire, which was given the U.S. Route 3 designation.