You and Other Drivers Safe in Congested Areas
Keep a Space Cushion
When traveling in congested traffic there can be frequent stops and starts. The vehicle in front of you may suddenly stop or swerve around an obstacle. It is important to give yourself enough distance to avoid a collision if this happens. Another name for this is a space cushion (not a space pillow - right). A space cushion gives you more time to perceive, stop or avoid a hazard.
The proper space cushion depends on the speed you are traveling and the driving conditions. At a minimum, you should use a 2 second space cushion for good driving conditions and moderate speeds. This is called the "2 second rule".