People do stop in the street and put in their hazards for various reasons, though. Legally or illegally, people stop in the street in front of businesses where there’s no parking and run in to get something; cars fail, or get flats. Especially with fender benders; even if there’s a shoulder, people justifiably put on their hazards. It may be less frequent than an emergency vehicle being in any given street at any given time, but in (US) metropolitan area it’s not uncommon.