About half a lifetime ago I worked in a building with a view of one of those bridges -- you know, the truck-eating bridge. In the case of this particular one, the bridge was labeled with a height of 13 feet 6 inches -- the legal height limit for trucks in Illinois. The problem was that over time, the City had used asphalt patching material to repair the deteriorating street surface, and had added about 4 inches of blacktop over the years. Thus, the "net" height was only 13 feet 2 inches -- low enough to catch about a truck per week. The added problem was that this was in a very bad neighborhood, so by the time the poor truck driver was able to get help and come back, his trailer was often vandalized and looted. Bad scene!