The U.S. National Highway Traffic Safety Administration stunned safety advocates by proposing new vehicle design rules that it says will help reduce pedestrian deaths. The rules will likely change vehicle design permanently.
As it is the US has no pedestrian safety standards at the federal level. I'm pretty sure if GM wanted to put out a truck with running chainsaws all over it then it would be perfectly legal as far as the NHTSA is concerned, although some state regulators might have a problem with it which is probably why it doesn't happen in reality.