In the context of cars and speed, as a professionally trained defensive/escape/evasion driver, safe following distance is the key to being able to react to just about anything on a fast highway. What a driver needs is room to react, 2-4 feet behind the car in front of you at 60+ mph and you're a statistic just waiting to happen. With our increasing density on the highways, this room to move is more and more difficult to come by. That, and move out of the passing lane fer pity's sake.
Just like biking, don't overlap and give yourself enough room to react to changing conditions. Being defensive doesn't mean slow, it means being ready.
Typical formula suggest two seconds of open road between you and the car in front of you... good luck getting that much room on an urban expressway these days.