Can I end with this - and another word for perish?

You are right to question your use of 'perished away' because it doesn't work. You don't say something perished AWAY...it just perished. That is if you intend it to mean 'died'--but you don't mean 'died' here so perish isn't the word to use at all. How about "night drew near, and trucks no longer rolled along the highway"?? (Or if you are referring to the fact that it is getting dark rather than traffic decreasing, you might say, "as night drew near trucks rolling down the highway were quick to p into the darkness and out of sight")