Hey. In 1973 our fantastic government passed a law that bumpers should be rated for a 5mph incident without damaging the lighting system and body. This is when we lost the tail lights in the bumper look. The law started out as 2 1/2 mph, but when it was passed it was 5mph. Now this is what I have read somewhere, but I could not find it again, in a 2 minute search to answer your question. GM was designing the 73 and up Colonade A Body line, as well as other news cars, and they incorporated a 10 mph bumper system in case the law was changed. This way they wouldn’t have to make any more changes. You have to remember that during the’70’s the auto makers where like beaten down dogs. Just take a look at a mid 70’s Mercedes 2 door coupe. The bumpers on that thing look like gutters from your house. The funny thing is the 10mph bumper law never came and in the early 80’s the law changed again so bumpers got smaller. Long story short, they never needed to be that big in the first place. Here is a neat article about the bumpers and what you can do to fix the problem. One of the cars is even a Laguna.