Route 140 is a 107.8-mile (173.5 km) long state highway which passes through parts of southeastern and central Massachusetts. The highway follows a southeast-northwest trajectory, running from U.S. Route 6 in New Bedford just north of Buzzards Bay northwest to an intersection with Massachusetts Route 12 in Winchendon, a few miles south of the border with New Hampshire.

The southern 19 miles (30 km) of Route 140 runs as a freeway between New Bedford and Taunton south from exit 12 off Route 24 to its southern terminus at US-6.

Route 140 begins at an intersection with US Route 6 (Kempton Street) and Brownell Avenue in Downtown New Bedford. This intersection is signed as Exit 1 when traveling southbound on Route 140, but the exit number has no meaning when traveling northbound. About a mile north, Route 140 comes to its first interchange, a cloverleaf with Interstate 195, which connects Providence to Cape Cod. Route 140 then curves slightly to the right to avoid New Bedford Regional Airport, which is accessible from the Hathaway Road exit (#3). Route 140 eventually leaves New Bedford and enters East Freetown, providing an exit that drops off near the center of the village. Route 140 then runs parallel to Long Pond before curving slightly west. The freeway section of Route 140 ends a few miles north at Exit 12, which is for Route 24. Meanwhile, Route 140 runs along County Street towards downtown Taunton.

The New Bedford Expressway has 12 numbered interchanges. The southbound intersection with U.S. Route 6, despite being an at-grade intersection, is signed as Exit 1 on the overhead guide sign. The I-195 interchange was formerly signed as Exits 2E and 2W, but have been resigned as Exits 2A and 2B. Likewise, the interchange with Route 24 formerly signed Exits 12N and 12S are now signed as Exits 12A and 12B.

The section of Route 140 was Widened to 4 Lanes and Realigned in Franklin. The $22 Million Project was Completed in 2007. In fall 2011, the ramp got finished from 140 to 495 South at 495s exit 17.

MA-140 runs partially concurrent with MA-79 Truck. It is signed from Exit 10 (MA-79) to Exit 12. At Exit 12 it runs onto MA-24 where it meets its parent at Exit 9.

The section of modern Route 140 from West Boylston to Gardner was numbered Route 64 when it was first commissioned by 1933. By 1939, the entirety of the route was redesignated as Route 140, effectively extending existing 140 northeast (it had previously run from New Bedford and ended in Grafton).

Prior to the building of the freeway section, County Street (the section of road beginning at the Taunton River, and also known as County Road) brought the road southward through East Taunton, Berkley, Lakeville and East Freetown. The road, which runs parallel to the freeway and crosses it in Lakeville, merged with Route 18 in East Freetown, just north of the New Bedford city limits. The old alignment begins in front of the Silver City Galleria in Taunton.