That rule of thumb gives you about a second, assuming no one cuts into your lane or crosses the median. You are reducing but not eliminating risk enough to emphasize that it’s not risky.
Yes, but it is a floor, not a ceiling. That's why I said "at least 1 car length".
I give as much space as I possibly can in following distance without impeding traffic, but not less than 1cl/10mph.
For example, if someone merges in front of me at approximately 3 car lengths at 65mph, I'm not going to slam on my brakes to increase the gap, then gun it back up to speed. That's dangerous. I'm going to get off the throttle, maybe brake a bit, and let the gap grow out before reapplying power, which gives me reasonable protection without endangering me too much. This is also much more predictable for cars behind me, which again is safer.
Not every situation is in perfect compliance with the rules. My goal is to maximize my safety, predictability, and compliance without causing traffic problems for others. That's why it's a rule of thumb. It's not written in stone, but it's a good guideline to start.
Yes, but you said that turning back to look is _not_ risky and only gave one number that is too close to look back without risk. Theoretically “at least” has no upper bound, which I suppose gives you an out...
Well I admit, I never did the math on my rule of thumb. Perhaps it's time to revise it and give even more space. Maybe I've been, despite effort, still following too closely. Like I said, I try to give maximum space and be as responsible as possible. Not perfect though. I can still improve as a driver, as your math shows.
