The exception for emergency vehicles is just another rule. And even that rule can be more complex, like a police car could be not allowed to drive on railways.

The exception for emergency vehicles is just another rule. And even that rule can be more complex, like a police car could be not allowed to drive on railways. Or military rules that are above emergency vehicle exceptions. A police officer is not above the rules. And in the given case we had none of them. It was just one simple rule - no vehicles inside the park.