Sagamore to NH border via via Plymouth, Cohasset, Hingham, Quincy, Boston, Burlington, Tyngsboro, Billerica and Lowell.
Brief multiplex with MA 113 in Tyngsborough.
Cosigned with MA 129 in Billerica.
Multiplexed with MA 62 in Burlington.
Cosigned with MA 139 in Marshfield.
Secretly cosigned on US 3 / MA 3 from Burlington to Quincy.
I originally thought this was a split route because the 3A designation piggybacks on route 3 for most of its course inside MA 128.
The southern portion was originally NE-6A. In 1933, southern 3A existed between Kingston and Quincy as it does now. By 1956, the section of MA 3 south of Kingston had become 3A.
The northern 3A makes its first appearance between 1942 and 1946, as US 3 is re-routed onto a new road bypassing Lowell. Between 1953 and 1956, US 3 became a highway and 3A was extended to include all of the former US 3 routing.