Recent transplants to Boston could be forgiven for thinking we have but one harbor tunnel connecting downtown with East Boston. The twinned Sumner and Callahan tunnels were in fact built decades apart, starting with the Sumner in 1934. With increasing volume, a single tunnel with traffic moving in each direction proved inadequate. So workers toiled 24 hours a day, six days a week crafting 14,500 tons of steel into the nearly mile-long tunnel to create the Callahan in 1961.
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