Massachusetts Route 3

Route 3 is a state-numbered route in the U.S. state of Massachusetts, maintained by the Massachusetts Department of Transportation (MassDOT). Spanning approximately 56 miles (90 km) along a north–south axis, it is inventoried with U.S. Route 3 (US 3) as a single route by the state. The state-numbered Route 3 travels from Bourne in the south to Cambridge in the north, while US 3 continues from Cambridge and crosses the New Hampshire state line in Tyngsborough. Mileposts on US 3 continue from those on the state-numbered Route 3.

Route 3 begins in the south as a freeway along a brief overlap with U.S. Route 6 (US 6) in Bourne. The highway is known as the Pilgrims Highway from Bourne to the Braintree Split at the Braintree–Quincy city line, where Route 3 meets with Interstate 93 (I-93) and U.S. Route 1 (US 1) and the three routes travel concurrently toward Boston as the Southeast Expressway. I-93, US 1, and Route 3 travel through the Central Artery and the O'Neill Tunnel in Downtown Boston, after which point Route 3 exits the concurrency and continues on surface streets. It crosses the Longfellow Bridge on the Boston–Cambridge city line, and transitions into US 3 shortly after an intersection with Route 2A in Cambridge.