i have bad news and good news.
the bad news is..
well, it's strange for dogs to run away from home.
i think the main reason is because if you were there,
and when the dog got hit you started yelling at it,
or maybe even just trying to catch it,
it thought you did it.
dogs are very complex sometimes.
my dog got hit by a car and when my mom went to go pick her up and rush her to the hospital, she was biting my mom off for about 3 minutes.
the dogs go through whats called trauma and shock.
they are in so much fear they forget things for a while.
the reason your dog ran away is because it was very scared and going through that stage where it was trying to hide from danger.
dogs aren't good at finding their homes but they will go where you always take them for walks, or the places they love most.
your dog will try its best to not to be visible to the human eye since it may be hurt, and knows it can't protect itself if so.
the good news is that ALL dogs come home before they die.
what i mean by that is,
if your dog was to die,
it would come to the front door,
dogs ALWAYS die at thier houses.
cats are the oposite.
anyways,
take care and good luck finding him!