RI border in Seekonk to Provincetown via Fall River, New Bedford, Buzzard’s Bay, Sagamore and Orleans.

Expressway/Super-2 from Sagamore to Orleans.

Brief multiplex with MA 114A in Seekonk.
Cosigned with MA 138 over the Taunton River between Somerset and Fall River.
Cosigned with MA 28 in Wareham and Bourne.
Multiplexed with MA 6A from Orleans to Truro.

Originally NE-3. US 6 came out of Rhode Island and ran pretty much as it does now to Sagamore via the Sagamore Bridge. East of Sagamore, it followed modern MA 6A to Orleans. North of Orleans, it still follows the same route it did in the past. Between 1950 and 1956 (see the 6A entry for more detail), the Mid-Cape highway was built and US 6 was placed onto it.

A 1966-67 map shows US 6 on both sides of the Cape Cod Canal. Some maps have shown this as US 6E and US 6W. Others indicate roads as one-way each; some avoid it by not putting any shield on the map between Bourne and Sagamore, and some simply put one US 6 shield onto both lines of the map. Sometme between 1989 and 1994, this was resolved. The road on the Cape side of the canal became part of 6A.