Changing A Landmark For Efficiency

by Don Friedman on August 19, 2016


There’s a proposal floating around to expand the walkway of the Brooklyn Bridge. In short: not enough width, too many pedestrians, and too many bicyclists. No one is at fault but one of the nicest walks in the city has been diminished by crowding. The basic idea is pretty simple: build more walkway on top of the truss bracing that extends over the driving lanes. I assume the extensions would be wood plank just like the existing pedestrian boardwalk.

The Brooklyn Bridge isn’t just a landmark: it’s one of first landmarks designated after the commission was created and it’s a National Historic Landmark as well. So changing it in any way other than repair is a sensitive topic. But in this case, I see no serious obstacle to the change for a simple reason: the current configuration of the deck is the third since the bridge was built.

The bridge has four main cables, two at the outer edges of the deck and two at the interior, separating the driving lanes from the elevated walkway. (Interestingly, the cables are not vertical. The curve of a suspension cable defines a plane and the planes of the interior cables are obviously tilted so that the pair are close together at the tower top but the walkway’s width apart at the deck. The outer cables’ planes are less clearly tilted but are also not quite vertical.) There are now four deck-stiffening trusses, one at each cable location, but there were originally six:

Period image, taken from “Cable Car Lines in New York and New Jersey” by Joe Thompson. Click on the picture for the original page. The elevated position of the walkway relative to the deck is clear.

When the bridge was built, there were half-height trusses at the outer edges of the deck (below the outer cables), full-height trusses at the walkway edges (below the inner cables), and full-height trusses separating the bridge railway from the driving lanes (not attached to any cables). This was version one of the deck.

The original cable-car bridge railway, which was simply a shuttle connecting terminals in downtown Brooklyn and near City Hall Park in Manhattan, was later connected to an elevated line, which had previously brought passengers from the outer reaches of Brooklyn to downtown Brooklyn and now could bring them across the river. In addition, streetcar rails were installed on the two inner driving lanes, providing further mass-transit capacity over the bridge. This was version two of the deck, with only one unencumbered driving lane in each direction.

From “Brooklyn Bridge: Historic Overview.” Click on picture for original page.

A reconstruction that ended in the mid-1950s removed both the streetcars and the elevated, removed the non-cable trusses, extended the outer trusses to full height, and put braces running horizontally across the driving lanes, connecting the tops of the walkway-edge trusses and the deck-edge trusses. That’s the third and current version of the deck.

The three versions of the Brooklyn Bridge deck are the top row of cross-sections. Taken from “What’s Your Brooklyn Bridge Ideal?” by Brad Aaron, on Streetsblog. Click on the picture for the original page.

So adding additional walkway space over the driving lanes would not be unprecedented, but rather be the third change to the deck since the bridge was built. And this proposed change would be exactly in the spirit of the previous changes: adapting the bridge to current patterns of use. A landmark that can’t be used is at best a work of art, at worst a butterfly pinned to a board. The best of preservation for a building (or a bridge) is to keep it alive and in use.

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