An elevated six lane highway was built in 1959 to bring the region’s interstates into the heart of Boston. During the 1960’s the main highway that weaved through downtown Boston comfortably supported a traffic volume of 75,000 cars per day.
While that was adequate in 1959, by the 1980’s the Central Artery was painfully carrying some 200,000 cars a day. As traffic slowed to a crawl for more than 10 hours everyday, the Massachusetts Turnpike Authority had to deal with an accident rate four times that of the national average for urban interstates at the time.
The Central Artery was not the only Boston thoroughfare that had experienced dangerous amounts of congestion during the last half of the 20th Century. The two tunnels that spanned under Boston Harbor between the downtown district and East Boston, and from downtown to Logan Airport also experienced excessive delays.
The Remedy to Boston's Problem
The solution to such a large and inevitable problem was the construction of the biggest, most costly project undertaken in the United States in all its history. Plans were drawn to replace the elevated six-lane Central Artery with an underground tunnel, eight-to-ten-lanes wide. This replacement would connect in the North to two bridge crossings 14-lanes wide, one of which would be a completely unique hybrid cable stayed bridge over the Charles River.
The project also called for the underground expressway, which would follow the same course as the Central Artery, to be extended beyond the point where the elevated highway once ended in downtown Boston to a connection with the Ted Williams Tunnel. The Tunnel would then carry commuters below the harbor to Logan Airport. In the end, the massive overhaul of Boston’s highway system would involve four expressway interchanges, mostly underground, and offer 28 different routes for motorists to enter or leave the city.
Perhaps the most noticeable of all the improvements to Boston’s transportation woes, the Leonard P. Zakim Bunker Hill Bridge emerges from the subterranean Central Artery crossing 1,432 feet of the Charles River to connect with I-93 and Massachusetts Route 1. The bridge is the only one of its kind in both design and scope with 8 central lanes running between dual cable arrays and the legs of 2 inverted Y-shaped towers along with a 2 lane cantilever to one side. The Bunker Hill Bridge is the only bridge in the world to have an asymmetrical longitudinal design as well as fuse together concrete and steel construction.
The most crucial piece of the CA/T Project was the process of expanding the Central Artery and placing it 120 feet below Boston’s surface roads. That submergence of the CA became the Thomas P. O’Neill Jr. Tunnel. Following the course of the original CA, the tunnel takes I-93 under downtown for a course of 1.5 miles.
Going beyond the CA’s endpoint, the tunnel, through the use of four interchanges, gives passengers the option of going North over the Charles River crossings or South to the Ted Williams Tunnel. The Ted Williams Tunnel was one of the first projects to be completed and opened to the general public. Named after the legendary Red Sox baseball player, the tunnel expands Boston’s travel capacity under the harbor from four to eight lanes.
Unfortunately, no one could have predicted the outcome of such a large endeavor.
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