We have shot a doe and buck this year walking a fence no more than 10 yards from the truck as they walked by. It all depends on how many cars they see a day and what distance. If there area a lot of cars around and they see them many times a day it won't matter. If you are hunting an area where there aren't many cars then they most likely will get a little spooky. 400 yards though I really wouldn't worry, thats a long distance off.