The two-second rule is a
rule of thumb by which a driver may maintain a
safe trailing distance at any speed. The rule is that a driver should ideally stay at least two seconds behind any vehicle that is directly in front of his or her vehicle. It is intended for automobiles, although its general principle applies to other types of vehicles. Some areas recommend a three-second rule instead of a two-second rule to give an additional buffer.
The rule is not a guide to safe ''stopping'' distance, it is more a guide to reaction times. The two-second rule tells a
defensive driver the ''minimum'' distance needed to reduce the risk of collision under ideal driving conditions. The allotted two-seconds is a safety buffer, to allow the following driver time to respond. The practice has been shown to considerably reduce the risk of collision and also the severity of any injuries if a collision occurs. It also helps to avoid
tailgating
Tailgating is the action of a driver driving behind another vehicle while not leaving sufficient distance to stop without causing a collision if the vehicle in front stops suddenly.
The safe distance for following another vehicle varies depend ...
and
road rage
Road rage is aggressive or angry behavior exhibited by motorists. These behaviors include rude and verbal insults, yelling, physical threats or dangerous driving methods targeted at other drivers, pedestrians or cyclists in an effort to intimi ...
for all drivers.
A large risk of tailgating is the collision avoidance time being much less than the driver reaction time. Driving instructors advocate that drivers always use the "two-second rule" regardless of speed or the type of road. During adverse
weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
, downhill slopes, or hazardous conditions such as
black ice
Black ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. The typically low leve ...
, it is important to maintain an even greater distance.
Application
The two-second rule is useful as it can be applied to any speed. Drivers can find it difficult to estimate the correct distance from the car in front, let alone remember the
stopping distance
Stopping sight distance is one of several types of sight distance used in road design. It is a near worst-case distance a vehicle driver needs to be able to see in order to have room to stop before colliding with something in the road