Mostly Funct

Unlike yesterday‘s remnants of a bridge, here’s a bridge that’s intact although not quite what it once was. Yesterday’s abandoned bridge, the Northern Avenue Bridge, was the northernmost over Fort Point Channel in Boston, just south of where the channel meets the harbor. A block south of that is its replacement, at Seaport Boulevard. A few blocks south of that is the Congress Street Bridge, and a block south of that is the Summer Street Bridge:

The sign says 1899 and that is when the bridge opened. The gable trusses carry the center span, which was retractable, with the westbound lanes on the north half moving to the north when the bridge was opened, and the eastbound lanes to the south moving south. The two halves moved separately using, more or less, steel wheels on tracks. Here’s a 1925 aerial view that shows the tracks on either side:

It’s not the most space-efficient form of movable bridge. The rolling bascules popular in Chicago, and the center-pivots on the Harlem River take up less space, but this side-retraction bridge is structurally simpler. In any case, it’s been locked in position since 1959, and the paving no longer shows any sign of the former moveable span, which makes the gable trusses look sort of undersized.