I just check how many dashes on the highway... the distance from the beginning of one "dash" to the beginning of another is 40 feet... So at 70 mph you need at

I just check how many dashes on the highway... the distance from the beginning of one "dash" to the beginning of another is 40 feet... So at 70 mph you need at least 5 dashes. The two-second rule is definitely the bare minimum... At 70mph that's 210 ft/s, and depending on whether the car in front of you can stop faster, that might not be enough distance.