The way it was

Here's another look at the former parking lot(s) at the foot of the Mont Saint-Michel. They're now mostly gone. Visitors to the island are required to park on the mainland and take shuttles over a newly (since 2014) constructed bridge. Now the bay's tidal waters can surround the island, and the movement of the tides and the adjoining Couesnon River can help to keep it that way by minimizing sedimentation. This view shows the tour bus parking area that is no more.

I count at least thirty buses in the lot. I get a different number each time I count.

I don't know the details, but there are residents on the island that must be permitted to drive, along with law enforcement and emergency vehicles, not to mention vehicles that provide services to businesses such as restaurants, hotels, and shops. I'll bet that access is tightly regulated.