Until you have a handle on that, perhaps you should just leave a bunch of extra space.

I have a handle on the amount of space I appreciate as a bicyclist, and that's what I give to other bicyclists. I don't know how many feet it is.

Accurately measuring feet with your eyes is hardly a prerequisite to safe driving. Do you measure your following distance in feet, or time & intuition for your own stopping speed?

Why not perform some measurements the next time you get on your bicycle, which might make you a better cyclist and driver?

I think that you probably know quite well how much space that is and are quite well able to estimate a 3 foot distance too. Nobody is asking you to maintain logs of your intra-vehicular distance for all your travels.

I don't necessarily disagree, but I would point out that there's a difference between knowing how much space there is relative to the likely movement of either vehicle (which is what's important for safety) and knowing how much space there is relative to a yardstick.

Obviously drivers should err on the side of more space. I have passed plenty of cyclists in an automobile, and I believe that I have always done so safely, but I can't confidently estimate the exact distance I put between the car and the cyclist.

Here is a good rule of thumb. Three feet is about the swing of a car door. If you can park next to another car and your passenger can get out without denting the car next to you that's three feet.

I commute by bike daily and 100s of cars a week manage to pass me safely. It is not that hard and has been common sense for 99% of all drivers who pass me even before this law. It is that one super-sized SUV who passes me with mere inches to spare while going 50 in a 35 zone.