I try and arrive at any State or Federal Park at least one hour prior to "opening" swinging open any drive through gates. An hours head start before the 1st traffic, mmmmmmmmmmmmmmm. Anytime a fee is involved and I can't find a person or pay box, I have the full fee ready to pull out and hand over immediately should someone show up. Hello Mr./Ms. Ranger, no I'm not trying to evade you. I have even been leaving in the morning, pull over and offer the fee and have an arriving attendant just wave me out with a smile.