Roadkill = Animals that have died on the road because of a collision with a car. That's why some American cars have huge "grills". It's sort of a protection for the passengers because it can get quite nasty when you hit a deer (or another big animal) at full speed. I've seen some pictures of those accidents and without proper protection I'm sure it could be lethal for the passengers. (Just use google images and search for 'roadkill')

you mean road killer? or rock you? the first one means a person whose drive skill so bad. the second one means rock the music