Does a three foot passing law actually require drivers to give three feet?
This may not seem very concrete to you, but if you think about it, it is very powerful indeed.

Imagine a collision between a car and a bike. With no such law in place you might expect there to be some argument about whose fault it was etc. etc. and as cyclists we all know from experience who's likely to come off worst...

However you put such a law in place and when you have a collision, the motorist has broken the law by default because they couldn't have been the required distance. I'm sure there would be circumstances where the motorist could argue that the cyclist was riding like a dick, but they would be forced to make that argument, you wouldn't start from a 50/50 position.

People have been talking about this kind of thing in the UK for years in order to make cycling safer, but nothing has ever been done. In fact I think this is the first form of words I've seen that achieves this goal.