To me a vehicle carries a human or goods on the ground and movement is generated via mechanical action, powered by either by a motor or a human being. Motorbike, car, cycle, rowboat. Pushing or pulling the object without a mechanism does not count as these are just extensions of 'pedestrian', buggy, wagon, skateboard, ice skates. If it does not carry a human it does not count. Toy car, drone. If it is not touching the park, it is not 'on the park'. Commercial airliner, ISS. A non functioning object that used to be a vehicle is now art or a monument, so long it has been approved to be in the park as such. Otherwise it is littering.

Emergency vehicles are exempt, like police or ambulance.