If it takes about 145 feet to brake from 60 mph to zero, it will take about 580 feet to brake from 120 mph to zero. This is because distance varies at the square of speed, or 4 times as the speed doubles. The threshold to braking is where the tire is at its maximum ability to brake , just before wheel lock. If you lock up the rear tires, the back end will come around and the car will spin on its axis. If the front wheels lock up the car will not turn and you'll loose directional control.
Threshold braking is a finesse procedure .
It is not always applicable, but knowing the technique serves as a benchmark for distance required to brake. Your braking capability will give you a good parameter for speed judgment. Braking in traffic should include the ability to threshold brake and the awareness that people and conditions may alter the braking application. Threshold braking is the absolute quickest way to stop and it will give you a good reference from which to determine all stops. The distance required will vary for different vehicles and even for the same vehicle under changing conditions.