6 month old jack russell afraid of being outside?

I am having a very serious problem with my 6 month old JRT. A garbage truck came down my street yesterday and scared the daylight out of my dog. Since then he absolutely freaks out whenever i take him out. His tail goes between his legs and he constantly pulls back towards my apartment. He has always been afraid of passing cars and I can't seem to break him out of it. I was able to walk him around the apartment complex avoiding the streets but now, no matter where I take him he goes nuts. He is even starting to go to the bathroom in the apartment again because he can't calm down enough to go outside. I just brought him back in and he fell right to sleep where normally he would be extremely energetic. I don't coddle him when he goes nuts or pay any attention to his behavior because I don't want to reinforce his fear but I am at a loss for what to do.