Page "Big Dig" Paragraph 16

A major reason for the all-day congestion was that the Central Artery carried not only north – south traffic, but much east – west traffic as well.

Boston's Logan Airport lies across Boston Harbor in East Boston, and before the Big Dig the only access from downtown was through the paired Callahan and Sumner tunnels.

Traffic on the major highways from west of Boston — the Massachusetts Turnpike and Storrow Drive — mostly traveled on portions of the Central Artery to reach these tunnels.

Getting between the Central Artery and the tunnels involved short diversions onto city streets, increasing local congestion.