If I can't use my horn "while stationary on the road", how do I tell the person in front of me to wake up from their cell phone and see that the light has turned green? /s

In Florida USA, the law changed within the last decade to remove the restrictions on vehicle horn use.

@PeterM why do you think a person using a cell phone while driving isn’t posing a danger?

@DaleM They're not driving per se. They're stopped, in a location where stopping is expected. And while they're being an ignorant what ever, they are not currently posing a danger to anyone. It would be a different story if they were doing the same while their car was moving.

@PeterM it’s still illegal in most jurisdictions- driving means being in control of a vehicle irrespective of it it’s moving

@DaleM You just moved the goal posts from posing a danger to being illegal

@PeterM someone acting illegally on the road is prima facie dangerous

@DaleM 20 mph over the speed limit in the US is illegal. Doing so on an otherwise completely empty freeway on a long straight section is not dangerous. However doing so in a school zone when school is letting out is dangerous. And in fact the cops won't even bother pull you over for doing up to 10 mph over the limit on a freeway - so they don't even think illegal is dangerous

@DaleM for what it's worth. Using your phone while being stationary (i.e. waiting for the traffic light to turn green, stuck in traffic jam) is allowed in the Netherlands. I don't know about other countries but I wouldn't be so sure about it being illegal in most jurisdictions. See government.nl/topics/mobility-public-transport-and-road-safe‌​ty/…

If I can't use my horn "while stationary on the road", how do I warn someone who is backing and about to collide with my car? This situation happened during a driving lesson when I was learning, and the instructor leaned over to press the horn. (Netherlands)

@gerrit ".... except when another road user poses a danger."

@IvoBeckers It's illegal in the UK. Rule 149: You MUST NOT pick up and use your hand-held phone or similar device while stationary in traffic.

@PeterM If you need a reason why it's dangerous, there's the simple reason you don't know what's happening around. Can't see a cyclist roll up to your blindspot. Can't see a runaway vehicle come straight at you. Can't see an emergency vehicle telling you to get out of the way. You can't react to a danger if you're looking at your phone, and danger can happen even when you're stopped.

@gerrit, this happened to me as a novice driver and I was actually hit by the backing car. I just couldn't find the horn quick enough. Since then I learned to be very quick.. I guess this rule is to stop cars to use horn in traffic jams. But I don't care about the written rule if I see any danger. Also this is a US rule, not universal as you stated.

This is not the place to argue personal opinions on what counts as "poses a danger". You may cite a judicial ruling or another law. It is only a judge that will decide whether you are correct to have honked, if UK courts work anything like I think they do.

The point of this law is not to micromanage the definition of "danger". It's to prohibit things like using the horn to let someone in a house know that you've arrived to pick them up.

@fred_dot_u Florida also just recently made it legal to hit protesters with your car if they're in your way. I wouldn't use anything done here as a precedent. (Currently living in Florida and mildly terrified of what's happening here.)

@DarrelHoffman: Out of curiosity, protesters or rioters? Many people confuse the term, but there's a huge difference between a legal protest and a lawless riot. The fact that someone is waving a sign does not in and of itself imply that they would pose a deadly threat to a motorist, but if rioters are throwing bricks, etc. anyone who acts deliberately to prevent a motorist from fleeing such a scene could be viewed as a deadly threat.

@Barmar: Also, I think the prohibition against honking when stationary only applies in built-up areas, and only in the hours between 11:30pm and 7:00am. If one blasts the horn in the middle of a residential area at 3:00am, even if it's to suggest that a motorist start moving, one might run afoul of the letter and spirit of the law, though perhaps a very gentle toot might fit within the spirit.

@supercat True -- I'm sure the police will take note of the actual circumstances.

@supercat The difference often depends on which side you're on. Our governor is quick to refer to any protesters he disagrees with as "lawless rioters" and any rioters he agrees with as "lawful protesters". So - yay democracy?