Never tried it but... 1. use a tri pod and make sure it doesn't move. 2. footage of the car driving by. 3. greenscreen footage of your actor pretending to get hit. 4. composite the actor and car footage together. or, this will take longer to do. 1. same as above. 2. same as above. 3. have a short clip of the actor walking then pretending to get hit near the spot where the car should be traveling. 4. no keying out a greenscreen but it will take some masking. Use a "garbage matte" because it will follow quad animation if you want the actor to fly off the screen in any direction you choose or if you want to make the actor look like he flips over the car or something. Regular masks don't follow the quad. I found that out the hard way.