After World War II, the East Boston Traffic Tunnel, also known as the Sumner Tunnel, was often gridlocked - being the only direct car route between Boston Proper and East Boston. The photo is from a 1947 report by a rapid-transit commission established by the state legislature, and has this caption:
This typical congestion will undoubtedly increase with the accelerated postwar production of automobiles. To attempt to route additional public transport vehicles through this tunnel would further add to the problem. Much of the congestion can be relieved by an extended and improved rapid transit system. Good public transportation would result in many of these cars remaining in their garages as the owners would undoubtedly make use of the improved rapid transit facilities.
In modern terms, the commission proposed a series of expansions that included an Orange Line running from Dedham to Reading, via Readville, a Red Line from Braintree to Lexington, a new Green Line branch to Needham via Riverside and an extension from Lechmere to Woburn and a Blue Line between Bowdoin and Lynn (the Globe's Emily Sweeney has posted a map of the proposed expanded system and wrote about what happened to the plan).
The proposal also called for incorporating subway tracks in the construction of a new bridge across the Mystic River to Chelsea - a bridge that would eventually be named for the governor at the time, Maurice Tobin.
The commission was so optimistic about all the people who would ride the new system - once it was taken over by a state agency from the old Boston Elevated Railway company - that it said cities and towns could yank up all those annoying trolley tracks clogging up thoroughfares like Mass. Ave. in Cambridge:
The Red Line, of course, was extended to Braintree and, if not to Lexington, at least the Arlington line. The Green Line now runs to Riverside. But the Orange Line, although relocated, still terminates at Forest Hills and no subway tracks were ever laid on the Tobin - people who want to take rapid transit to Chelsea can take a bus that is frequently delayed because it goes over a drawbridge across busy Chelsea Creek.
Boston Harbor, meanwhile, now has three tunnels for cars and trucks - the Callahan opened in 1961 and the Ted Williams to trucks and cabs in 1995 and to cars in 2003.