feeds onto the Leverett Circle Connector bridge. Former exit 22 continued to exist as an offramp to Chinatown from the southbound (former northbound) Dewey Square tunnel until the ramp was closed off in 2004. 23 exists both northbound (now new exit 17) and southbound (now new exit 16B) and leads to the Scollay Square area. 17A-B southbound (formerly exit 24) now exits to Haymarket Square and MA-1A (the Callahan Tunnel). Much of the reconfiguration of on and offramps (particularly the wide separations of the ramps for exits 16 and 18) was done to move exiting traffic off the mainline of the road, reducing stress on the mainline. Pre-Big Dig The entire route was in Boston, Suffolk County. Post-Big Dig The entire route is in Boston, Suffolk County. Exit numbers on I-93 will eventually change to a mileage-based exit numbering as part of Massachusetts Exit Renumbering Project. Numbering Currently, the Artery is numbered I-93 and US 1 on the whole route, and Route 3 on all but the northernmost section—it leaves at exit 18 (former exit 26). The Artery has had many different route numbers through its history. When first built, the section between the Sumner Tunnel and Storrow Drive received the numbers C1 and C9 (city routes of US 1 and Route 9), which were rerouted off local streets. The rest of the highway was unnumbered, despite being closely paralleled by C37 south from the Sumner Tunnel. By 1969, I-95 was assigned to the whole Artery as part of its never-built route through Boston. The "C-prefixed" routes were removed in 1971, with Route C1 becoming part of a realigned US 1, using the Artery between Storrow Drive and the Sumner Tunnel. Additionally in 1971, Route 3 was moved from a bypass around downtown to use the Artery south of Storrow Drive and the Southeast Expressway. In 1974, I-95 was canceled through Boston (cancelling its approach from Providence, Rhode Island through the Southwest Corridor) and was instead rerouted around the city using part of Route 128. US 1 was realigned to use the Tobin Bridge and Northeast Expressway, which had been signed as part of I-95; thus US 1 used the Artery north of Storrow Drive. The former alignment of US 1 from Storrow Drive south along the Artery to the Sumner Tunnel became an extended 1A, and I-93 was extended south from Charlestown along the Artery, Southeast Expressway and Route