 Its northern terminus is at Exit 18 (Massachusetts Avenue) in South Boston, a former Y-interchange where the cancelled Inner Belt (I-695) was to meet with the expressway and the Central Artery.The southern terminus is at the Y-interchange (the "Braintree Split") at Exit 7 in Braintree (the former southern terminus of Route 128).A section of the Expressway, beginning south of the Savin Hill overpass and ending just before the Braintree Split utilizes a zipper lane, in which a movable barrier carves out a reversible high occupancy vehicle lane on the non-peak side of the highway during rush hour.