I just did the Stranger Things drive though event, I didn't see any real issues with people staying in their cars for an hour. Like what SFMM will do, there are bathrooms before it starts and after, and not during. And I didn't see anyone wandering outside cars that weren't supposed to be there. (At the Stranger Things drive through, they did mention that if you did have a problem during the event, to put on your hazard lights.)
I'd imagine there will be both crash barriers up at senstive points in the park to protect things, and security scattered thoughout to keep people in their cars and be available in case of emergency.