Route 1A is a north–south state highway in Massachusetts, United States. It is an alternate route to U.S. 1 with three signed sections and two unsigned sections where the highway is concurrent with its parent. Due to the reconfiguration of tunnel interchanges brought on by the completion of the Big Dig, Route 1A is discontinuous in the downtown Boston area. Vehicles entering Downtown Boston via the Sumner Tunnel must take I-93 north to the exit for Government Center and make a U-turn to access the entrance ramp to I-93 south and vice versa.

U.S. Route 1 (US 1) is a major north–south U.S. Route in the state of Massachusetts, traveling through Essex, Middlesex, Suffolk, Norfolk, and Bristol counties. The portion of US 1 south of Boston is also known as the Boston–Providence Turnpike, Washington Street, or the Norfolk and Bristol Turnpike, and portions north of Boston are known as the Northeast Expressway and the Newburyport Turnpike.