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The Two Second Gap

The two-second gap is a rule of thumb by which a driver can a safe distance behind the car in front at any speed. The gap is especially useful on the motorway, when many cars and heavy vehicles are traveling at high speed, and collisions can be vary serious, involving many cars. People measure the time between the car in front passing a landmark, and themselves passing it.

Often people find it easier to judge distances. The speed limit on the motorway is 70 miles per hour. At this speed, what distance would correspond to a two second gap?
\[70 mph = \frac{70 \times 1609}{3600} = 31.3m/s\]

In two seconds a vehicle traveling at 70 mph travels  
\[31.3 \times 2 = 61.6 m\]
  and many people find a distance like this easier to measure if there are no 'road furniture', like signs.

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