Flavors of Obsolescence

by Don Friedman on October 13, 2017

This article in Curbed gets the facts right but also, by accident, emphasizes a point of unclarity that has led to a lot of sensational headlines over the years. There are some 2000 bridges of various types in New York City, most of them small. It sounds horrifying that 76 percent are “functionally obsolete” and don’t meet current design standards…until you get to the statement that only 86 are structurally deficient.

First, 86 bridges that are structurally deficient is, to my mind, 86 too many. However, that doesn’t actually mean that any are unsafe. A bridge that is structurally deficient could simply have a reduced load capacity that means trucks can’t use it, for example. Not a good situation, but not unsafe.

More importantly, most of the 1500 or so bridges that are functionally obsolete are fine for current loading. They suffer from traffic design problems, such as too steep slopes, too narrow lanes, or curves with too-small radii. All of these are problems, but not structural incapacity; in nearly all cases the issues can be dealt with by simply reducing driving speed. That’s not great but ti’s also a lot less dangerous than it sounds.

In other words, the fact that 76 percent of our bridges is functionally obsolete is another way of saying that most of them were built long before current standards for road geometry were developed.

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