The only way to get a horse used to anything is to make it do it, Flip

Not all drivers are "as safe as the horse" I hate to say it, but that's rubbish. Not saying all drivers are bad and people have to realise this, but people also have to realise how driving centimetres away from a horse, beeping, or revving the engine is going to cause distress in the calmest of horses. To them, it's like a lion roaring right behind them!
Ned is fine in traffic, he doesn't spook when cars come whizzing past at 80MPH down a 60 road, he doesn't mind lorries or tractors, or even bikes! But what does scare him is what I just mentioned and Ned kicks. If you crawl right behind that horse, expect a dented bumper! I do warn drivers and I thank them when they pass us correctly and are polite (I thank too much, I think. I've thanked some right jerks)
But even screaming at the top of your lungs and making big hand gestures for a driver to back off sometimes doesn't work. (Don't worry, the screaming and waving my arms doesn't scare him)
I'm a good horse rider and can keep him under close control, but I shouldn't HAVE to battle with the poor animal, because someone can't keep a good distance. I've only lost him on the road once.
At my stables, when we have to take a youngster out to train it to get used to traffic, we ALWAYS wear a "YOUNG HORSE CAUTION" vest, which most drivers do take notice of. But of course, there's always people who think it's funny to see a terrified horse. Usually younger drivers trying to impress their friends. Those and people on the phone are the worst!
EDIT: Also, I will try and get some more footage on my helmet cam, to show you what roads I ride down and what kind of traffic I contend with.
R.I.P Annie, Holly, Spike, Louie, Mel, Robbie, Mr.H, Molly, Archie, Blobby and Dancer <3