Adequate Following Intervals

The need for adjustments in following time occurs when speed or road conditions change. The distance for steering is much shorter than it is for stopping (note: the heavier a vehicle is, the longer it takes to stop). Response time with the hands is close to ½ second while response time with the foot is normally ¾ second. This does not take into account any lag in perception time due to fatigue, drugs, or inattention, etc. All time and distance relationships are designed for the best driving conditions.

• A 2-second interval provides the driver time to steer out of problem areas at all listed speeds on a dry surface and braking out of problems at speeds less than 35 mph.
  
• A 3-second interval provides the driver time to steer out of problem areas at all listed speeds on dry surfaces and braking out of problems at speeds to 45 mph.
  
• A 4-second interval provides the driver time to steer out of problems at all listed speeds on dry surfaces and braking out of problems at speeds up to 70 mph.