Here in the USA, it has become ‘fashionable’ but dangerously inadequate for states to introduce laws requiring drivers to leave only three feet of space when passing a bicyclist. However, there are many circumstances, typically involving speed and/or the size of the vehicle, when passing that closely would at the very least be frightening for the person on the bicycle and at worst be downright dangerous.
The first bit of advice and legislation needs to be: If it’s not safe to pass a bicyclist because you can’t leave enough space for genuine safety then be patient and wait behind until it is safe. Remember, a driver’s convenience and selfish desire not to be delayed must never take priority over other people’s safety, ever!
Secondly, as implied above, the minimum safe passing distance needs to be significantly more than a mere three feet. As an example, Britain is now formalizing its guidelines, which have always unofficially been around six feet, and is now saying that the absolute minimum gap should be 1.5 meters, but larger where safely possible.
Compare the recommended 36 inches in the USA to the 59 inches in the UK — effectively three feet versus five feet — and then compare the vast difference between actual road safety results between the two countries. Britain for at least 30 years has typically vied with Sweden each year for who would have the safest roads in any developed country. The U.S., on the other hand, has always been in the bottom three of the ~30 member nations of the OECD — the group of developed nations that are checked against this standard every year — and has a road death rate over four times greater than the UK and Sweden. So which countries’ example do you think it might be better to follow?