> That is completely unrealistic.

Why is it unrealistic, besides the fact that you're following too close behind? If your line-of-sight is shorter than your braking distance, you are driving wrong.

Something more realistic then. Drive far enough behind the vehicle in front of you so that you can stop before falling down the same sinkhole/broken bridge/earthquake damaged overpass they just fell into.

Math seems to work out if you keep a 3 second distance to the car in front of you.

Google shows two-second rule when looking for "safe following distance" - I was taught 3 seconds and it seems more reasonable assuming slightly over a second reaction time.