Quote:
Originally Posted by ilusnforc
If you are 130 ft behind a vehicle that begins braking and it takes you 130 ft to react and begin braking as well, you will begin braking at approximately the same point as the vehicle in front of you, if you have better braking capability or shorter stopping distance you will still be well behind that vehicle when stopped as the vehicle in front of you will be incapable of an instantaneous stop (except in the instance of something influencing the abrupt stopping of the vehicle in front of you such as the already mentioned reinforced wall, car hitting a stopped big rig, etc).
Assuming that average human reaction time from seeing a situation to applying brakes takes 130 ft, I'd say that 130+ ft is safe for a following distance.
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The problem there is that if the average is 130 ft before someone starts to brake, then some people will be above average and fine, and another large chunk will be below average and tap the semi on the rear. Having a safety margin is never a bad idea AFAIK, which is why we have the three second rule like you mentioned instead of a two second rule even though on average may be able to respond in two seconds.