Most utility companies have "bat phones" which connect the fire/police dispatch centers with the utility operations centers/radio rooms. The operations centers talk to each other constantly by radios and phones ensure no mistakes are made. I's called coordinated disaster planning, and it's been going on successfully for years, probably decades.
Police and fire departments receive regular training (usually from the utility companies themselves) on how to handle public safety situations involving electric utilities. If a policeman or fireman ever told a civilian to get out of the car without authorization from the utility, he would probably be severely disciplined or fired.
Something like 8000 police departments (and probably a similar number of fire departments) in the United States and you're asserting that all of them have such impeccably uniform training and high procedural standards that they will act equally prompt and correct during power line events? I was once stuck in traffic while a volunteer FD cordoned off a one block area because of a downed telephone cable. Heck, in many blue zone jurisdictions, police officers aren't even required to have a high school diploma, let alone training in power line event protocols. There's a reason that utility companies have roving trucks on call 24/7 - they aren't going to shut down even one square block of the grid on the say so of a cop or even a fire chief until somebody on their payroll has eyeballed the trouble. In the case of downed and severed power lines, automatic disconnects generally kick in. But to take a cop's say so on the matter makes as much sense as working on a high voltage circuit without a keyed lockout.