> The park could contain loose soil on the edge of a cliff, so any vehicle driving there could cause a landslide that topples the vehicle over the cliff and could kill anyone on the beach below. No vehicles in the park.

I live in a city with Trams. Whenever they replace tram rails they remove the surrounding concrete and asphalt. It would be dangerous to drive there. In those cases they explicitly hang a “road closed” sign with an extra sign “including service vehicles”.

In the real world signs (especially common ones) try to be reasonable descriptive. Nobody is helped if you argue about the meaning if something goes wrong.