Allow the user to add more than 1 emergency vehicle responding in the vehicles.json file.
Like the police, you could use additional modded or original vehicles to respond if you requested them. So if I wanted an ambulance, instead of spawning just the ambulance model, it could spawn ambulance2, ambulance3, quickresponse1, or other vehicles that someone may have added to the game.
Same thing with the firetrucks, tow trucks, etc.
I'm not this much of a programmer, but it would add a bit of realism as not every ambulance and firetruck are the same.