NYC takes the cake for inaccurate bridge height signs, though. Some bridges have signs indicating 12'9" or lower clearance when standard 13'6" trucks can clear them easily. It's a complete mystery why they can't mark them correctly. It's been this way for decades (literally).
About an hour and a half later, we established that the road had been recently re-paved and no one was exactly sure what the height was. Backing up to the nearest intersection was not an option because there were none close by and turning the tractor-trailer around was impossible. The cops were cool about it and suggested that I creep forward very slowly and see if I'd fit. I was able to do this and stop just as the trailer reached the bridge. I got out of the cab and climbed up behind the tractor to have a peek and had about an inch to spare. I went for it, very slowly, and made it under. No fun but I did get a cool photo as a memento: http://i.imgur.com/64uYu2z.jpg
I took a different route on the way back of course!