Full Stop Ahead
Traveling Speed On Dry Roads
Traveling Speed on Wet Roads
I think that the skid mark distances didn't double because of the fact that the wheels will rotate while you are hitting the breaks, but after a while, they will begin to lock. Thus causing the skid marks.
The maximum speed you should be driving is 44 miles per hour or less. This way, you won't exceed the length of what it would take to hit the car in front of you.