I was out with a crew last year when they came across parked vehicles which impeded the progress of the pump, although not on a call. A couple of us got off to put leaflets on the cars which aroused suspicion of some of those in a que outside a parcel office.
One chap asked why I had put a leaflet on his car (not a happy bunny as he had to leave the queue to move it). I informed him politely that he was obstructing the road, was illegally parked anyway and if he wished to make an issue of the matter, I would request the Police to attend, which meant he would have got a ticket.
He was not happy, but I did mention that in an emergency we need to get applinaces through and people like him don't help by inconsiderately parking. He apologised and told me he would be more thoughtful in the future. (Yeah, right!)
Even with publicity, leaflets on cars partnership working with the Police and education, the public really don't care that their naff parking may inconvenience crews attempting to get through because, even in their own streets, it's a "it'll never happen to me" attitude.
