Sure bridges take a while to build and plan, but there is also a demanding upkeep to a bridge. One of the most important upkeep is making sure the metal has a coating on it so that it can resist corrosion. Paint has been the old method of keeping corrosion away. Also when suspension bridges get some age on them the cables start to stretch and have to be replaced. There are some advances that are under development now such as wrapping the cables in a polyethylene pipe or making them out of graphite compound. All of these matters are taken into consideration after a bridge is built and technology is constantly improving bridge maintenance and safety.