I have to agree with Eissy. Hell hounds, I would say, is a poor term to use for the...creature you are referring to. It sounds like your talking about the mythical black dog that DeadPoet mentioned. Where did you hear this myth and why are you worried? Have you seen it three times? Less?
There is also another Myth, one a movie in America mentioned (though I can't remember what it was called) When your tiered, your eyes play tricks on you. It has happened to me many times, specially at night. I work at 3am, trust me when I say I have seen things that have made me slam on the breaks or swerve at times. Almost all cases it was my eyes. Truckers call this 'Devil Dog' or 'Demon Dog'. They see a black dog running at them while driving and jumping at the cab's windshield. When this happens, Truckers say they are very cautions because it usually means death is near. This is a myth though, derived from a few truckers who had hit and killed cars and people, saying they were trying to avoid the black dog in the road. Urban ledged really.