Hmmmmmm,
As a passenger on a Public Transportation Bus, she is still subject to arrest for failure to produce valid vehicle registration.
The purpose of posting those rules was to demonstrate that the road in question is not your typical public road. There are all sorts of restrictions that go along with the use of this road. You can't have alcohol in your vehicle. You can't have a weapon. You can bet your boots there is a sign at the entrance saying that all vehicles are subject to search.
It is not like this woman is on a city bus on a public road and they are asking for ID out of the blue. They ID everybody who comes into this place, whether they drive, bike, walk or ride the bus.
I suppose they could stop the bus and check all IDs before letting the bus in through the gate, but that would just delay things and the additional delay would serve no purpose. But then nobody could pretend that this was happening on a typical bus route.