Big Dig - Impact On Traffic

Impact On Traffic

Before the Big Dig, the Central Artery carried not only north–south traffic but much east–west traffic, a major cause of its all-day congestion. The only direct access to Boston's Logan Airport from downtown was through the paired Callahan and Sumner tunnels under Boston Harbor. To reach these tunnels, traffic on the major highways from west of Boston—the Massachusetts Turnpike and Storrow Drive—traveled on portions of the Central Artery. Getting between the Central Artery and the tunnels also involved short stretches on city streets, increasing local congestion and causing backups on the highway.

The Big Dig untangled this co-mingled traffic. While only one net lane in each direction was added to the north–south I-93, several new east–west lanes became available. East–west traffic on the Massachusetts Turnpike/I-90 now proceeds directly through the Ted Williams Tunnel to Logan Airport and Route 1A beyond. Traffic between Storrow Drive and the Callahan and Sumner Tunnels still uses a short portion of I-93, but additional lanes and direct connections are provided for this traffic.

The result was a 62% reduction in vehicle hours of travel on I-93, the airport tunnels, and the connection from Storrow Drive, from an average 38,200 hours per day before construction (1994–1995) to 14,800 hours per day in 2004–2005, after the project was largely complete. The savings for travelers was estimated at $166 million annually in the same 2004–2005 time frame. Travel times on the Central Artery northbound during the afternoon peak hour were reduced 85.6%.

A 2008 Boston Globe report asserted that waiting time for the majority of trips actually increased as a result of demand induced by the increased road capacity. Because more drivers were opting to use the new roads, traffic bottlenecks were only pushed outward from the city, not reduced or eliminated (although some trips are now faster). The report states, "Ultimately, many motorists going to and from the suburbs at peak rush hours are spending more time stuck in traffic, not less." The Globe also asserted that their analysis provides a fuller picture of the traffic situation than a state-commissioned study done two years ago, in which the Big Dig was credited with helping to save at least $167 million a year by increasing economic productivity and decreasing motor vehicle operating costs. That study did not look at highways outside the Big Dig construction area and did not take into account new congestion elsewhere.