Massachusetts Route 20A

U.S. Route 20
Map of Massachusetts with US 20 highlighted in red
Route information
Maintained by MassDOT
Length:	153.44 mi (246.94 km)
Existed:	1926 – present
Major junctions
West end:	US 20 at the New York state line in Hancock
	US 7 in Pittsfield / Lenox I‑90 / Mass Pike in Lee US 202 / Route 10 in Westfield US 5 in West Springfield I‑91 / I‑291 in Springfield I‑84 in Sturbridge I‑290 / I‑395 in Auburn Route 146 in Millbury I‑495 in Marlborough I‑95 / Route 128 in Waltham
East end:	Route 2 in Boston
Highway system
United States Numbered Highway System List Special Divided Replaced Massachusetts State Highway System Interstate US State ← Route 19 Route 21 → ← Route 4 N.E. Route 6 →

The cross-country U.S. Route 20 runs its easternmost 153 miles (246 km) in the U.S. state of Massachusetts. The highway crosses the state border from New Lebanon, New York into Hancock, Massachusetts, and runs eastward into Boston, where it ends at Route 2 in Kenmore Square. It spends the vast majority of its journey paralleling the Massachusetts Turnpike, which has largely superseded US-20 for through travel. Still, US-20 directly serves many towns and local business areas which the Turnpike bypasses.

U.S. Route 20 is the longest numbered highway in the entire country and also holds the distinction of being the longest numbered highway in the state, edging out Route 28 by merely a mile (Route 28 is 151.92 miles (244.49 km) long).

Parts of US 20 between the Worcester and Boston areas were also an alignment of the Boston Post Road, an early colonial highway designated in 1673 for carrying mail between New York City and Boston. US 20 is still locally known as the "Boston Post Road" in the towns of Marlborough, Sudbury, Wayland, and Weston.

U.S. Route 20 begins its eastward trek crossing the New York state border into Hancock, Massachusetts, passing through the southern edge of the Pittsfield State Forest before entering Pittsfield and meeting the northern end of Route 41. The highway enters town and meets U.S. Route 7, near the western end of the cross-state Route 9. US-20 turns south along US-7, and the two routes form a concurrency into the town of Lenox. In Lenox, Route 7A splits off to serve the center of town, and US-20 splits from US-7 shortly thereafter to serve the town of Lee to the southeast. The highway passes through town and interchanges with the Mass Pike at Exit 2 south of town, near the eastern end of Route 102. US-20 turns to the east at this point, and closely parallels the Mass Pike for several miles, before entering the town of Becket and meeting Route 8. Route 8 northbound joins US-20 east to directly serve the town, while the Mass Pike passes south of Becket. Upon crossing through the town center, Route 8 splits from US-20, and the federal highway continues eastbound, passing into the town of Chester in Hampden County.