By the time you use your horn it's too late for the most common fatal multi-vehicle accidents, which are crossing traffic incidents. Most motorcycle saftey courses tell you not to bother with the horn until you have the incident under control because people don't react predictably or in time to horns.
amazing number of downvotes on 'horn' -- actually, as an urban rider, the horn is very useful. Plenty of comments here have to do with the freeway or during an event that has already started.. thats not the purpose of a horn. The horn is to tell others you are there before an accident starts, in a setting where they can hear you. Amazing antipathy for a safety statement here..
What? You honk your horn every time you enter an intersection where a driver is present and could cross your path? Because if they're already crossing your path then honking your horn is the last thing you should be concerned with.
Then maybe you should explain what you're actually doing because I'm an urban rider, my friends are urban riders, and the general consensus in our local motorcycling community is the horn is useless. Because like I said, if the driver isn't crossing your path then there's no reason to sound the alarm and if they're already entering/crossing your path then you'd better be engaged in crash avoidance. It's not clear when you're using your horn.
