The van which follows the car the characters are in goes down a different road and then gets out of sight for an undetermined length of time, and is not in sight when they make their final turn. There is no plausible way for the driver of the van to know which way they went.
At the beginning when they are passed by the van on Storm King Mountain Road, they are traveling south towards the city, instead of north towards the Catskills. You can tell this by the Hudson River being on the left side of the road, instead of the right.