Where is vehicle reservation on Web sight?

I think the easiest way is to call, sometimes the reservations are not updated online

Well if your taking about a reservation for a camper then yes you can book that on the website but if your talking about getting your ATV registered for riding you have to do that there when you check in. You can do it at the Trailhead office, you can get passes for both of the trail systems they have but you have to do it in person.