The braking distance at 70mph is a huge 75m, which is about 9 London buses. Add your reaction time, and do you aee why distances of over 100m between cars are slightly unrealistic?
In the event of a pileup, it doesn’t really matter how much distance you’ve left. If you end up hitting the car in front of you, you get cited for failure to maintain distance. Because, if you had left enough distance, you wouldn’t have hit the car in front of you. It doesn’t matter if you left 50, 75, or 100m. If you hit the car in front, you didn’t leave enough space. And the risk of someone else swerving into that gap doesn’t mean you’re not at fault, it just means you’re both wrong now.
> In the event of a pileup, it doesn’t really matter how much distance you’ve left.
For legal liability, that might be true. In reality, if you've left yourself a safe amount of distance, you have more opportunity to react to events in front of you in such a way that you minimize damage and loss of life (thus mattering).
Even if you still crash, the extra second of braking time can take off ~10-15 mph [0], which at 60 mph V(t=0) is ~40% of the energy that would otherwise dissipate into your car and the cars you hit.
No, at 70mph (31m/s) you travel 100 metres in 3.2 seconds. I was always taught 3 seconds on the highway is a safe following distance, and 4 seconds in adverse weather conditions like rain.
> Allow at least two seconds' following distance behind other vehicles in good weather and road conditions (three seconds on a highway).
> Slow down for poor weather conditions or uneven roads and increase your following distance to at least four seconds. Remember that the distance required to stop increases in wet or slippery conditions.
