Honestly, when you're driving, you sometimes only see the car in front of you. You might see it slowing down first, and you start slowing down, or continue because there is enough distance anyway. Then the car in front of you stops abruptly or crashes. Now you panic and brake hard. Maybe you still crash into the car in front. Even if you stop before crashing, this hard braking causes the car behind you to crash into you.
TL;DR - Sometimes the 3 second following distance is just not enough even if someone is paying attention because they can only see the car in front of them.
> You might see it slowing down first, and you start slowing down, or continue because there is enough distance anyway.
That's the thing, though - if you were already at the distance limit, and the car in front of you starts slowing down, you have to also start slowing down right away to maintain said limit. If you do not, then it's already "not enough distance" by definition at that point, and you're the one responsible for that.
>TL;DR - Sometimes the 3 second following distance is just not enough even if someone is paying attention because they can only see the car in front of them.
Yep... the usual advice locally is 5 to 7 seconds gap for freeways and similar, before accounting for weather and other conditions. Of course, that assumes you can leave a gap without some bastard deciding to sneak in and occupy it.
> without some bastard deciding to sneak in and occupy it
Unfortunately, this. It sucks to keep a larger gap, have some idiot sneak in, and now you have to brake to maintain the distance again, repeat. FWIW, I am very careful to maintain distance just for situations like the one in this post.
On this bridge you're always going to have someone occupying open space, but you can still maintain 5 seconds of visible leading distance. Alas, a lot of drivers on this stretch of freeway are insane.
TL;DR - Sometimes the 3 second following distance is just not enough even if someone is paying attention because they can only see the car in front of them.