Could be an exception... or not. Some prohibitions come from hazards like "this won't hold your weight" or "this could flood unexpectedly". And there's no emergency vehicle exceptions.

I had my closest park in mind when answering. It has a river and multiple wooden bridges to access. Also, the ground floods sometimes in the winter and some paths are too soft for a car. No way an ambulance or firetruck is going to get in the park. They could try, but would loss more time than doing it on foot, or a bridge would collapse under their weight.