The "bumps" as they are colloquially known are, in fact, metal covers for expansion joints. Next time you go over the bridge, take a moment to peek over the side and take a look under a bump. You'll see a wide gap between adjacent sections of the bridge (the sections are technically termed "spans"). When working with material of excessive length that is exposed to temperature extremes (for example, bridge spans), one must make allowances for heat expansion and cold contraction. Otherwise, the bridge would buckle in the summer and separate in the winter. To get around this engineering necessity, bridge builders employ expansion joints, which usually are some form of collapsible material. In the case of the Williamsburg Bridge, the builders merely left gaps between the spans and placed metal covers over them.

So, these metal expansion joint covers, while structurally neccessary, are not the only possible solution. Indeed, a metal cover that sat flush with the bridge path or had a gently sloping profile would be much better. In fact, the reason you often don't notice the expansion joints on other bridges around the city is because they sit flush or are gently sloping. The covers on the W'burg bridge just happen to be poorly designed for their intended use. They're extrermely dangerous and, worse yet, illegal due to noncompliance with the ADA. There have been numerous injuries and (to my knowledge) 5 pending lawsuits as a direct result of these bumps. Recently, thanks to a raccous Community Board meeting, the DOT has consented to conduct a study (lame, but an important first step) on the safety of the bumps and feasinble alternatives. So progress, while slow, is existant.

Now, we often hear about supposed benefits of the bumps, usually that they prevent excessive speed. While that may be true, there are many other ways of controlling the speed of bridge path cyclists that don't physically injure close to 1 in 4 of ALL users. Signage, bollards, legitimate speed humps, etc could all be successfully employed without extracting such a terrifying penalty. Also, if you consider the other bridge paths around town that don't have dangerous obstacles on them, you quickly realize that the cyclists on those paths don't go screaming at 45 mph downhill, despite the lack of dubious speed controls.

Hope that helps

DGS