NY line in Pittsfield to Boston via Springfield, Auburn, Marlborough, Waltham and Watertown.
Cosigned with US 7 from Pittsfield to Lenox.
Cosigned with MA 8 east of West Becket.
Multiplexed with I-291 through Springfield.
Cosigned with MA 32 in Palmer.
Brief multiplex with MA 19 in Brimfield.
Cosigned with MA 12 in Auburn.
Cosigned with MA 2 briefly in Boston.
Originally NE-5. In 1930, US 20 took a more northern route from Palmer to Worcester, passing along what is now MA 67 and MA 9. East of Worcester, it originally passed through Shrewsbury in a more-or-less straight route into Northborough. By 1933, US 20 was onto its current routing.
The only other significant route changes are in the city of Springfield. Originally, US 20 crossed the river where MA 147 does now and then routed up State St to Boston Road. Between 1972 and 1974, US 20 was routed up I-291 to Page Blvd, where it took over MA 20A‘s routing to Boston Rd.
Dan Vincent’s US 20 page.