BACK ROADS by Joshua Scribner is a flash fiction about a guy driving home from college during a snowstorm. Every time Carter sees a cross on the side of the road, a new "passenger" joins him inside his vehicle. It's unclear if they know the driver is aware of their presence, but he can hear them plotting to attack, which causes Carter to drive rather recklessly.
There is more than one supernatural twist to this story, and while this short is entertaining as-is, I wish Scribner had given more background on the characters involved. Seems such a shame to use such an original idea on only a few pages.