I didnt reolise that the sound level of a truck driving was the same as a horn, thats because its not, its louder, I even bet they design them that way, ow wait they do.
I know trucks can be pretty loud, but I haven't heard any that are louder than their own horns.
If a vehicle runs over your neck in Yorkshire it's just as likely to kill you there than if the accident happened in Hammersmith. Just because you're in Hammersmith and the cyclist ahead has been overtaken by one vehicle in no way makes the rider any more aware of your vehicle than it would if you were in rural Yorkshire and no one had just passed them.
This is a very good point. I've learnt through experience that it's when there's a string of traffic that I'm more likely to make an error and not realise there's something about to pass me. If a lorry passes you, and there's a car behind it, the lorry's engine totally drowns out any noise the car is making. THAT would be a time when a quick beep of the horn (by the car driver) would actually be useful.
The thing is, I live in a country where a lot of drivers beep their horns when they're coming up behind a cyclist, on an otherwise empty road in the middle of nowhere, and it doesn't make the roads any safer. When you hear a lot of beeping, it just becomes background noise, and no-one takes a blind bit of notice.