<P> Some authorities regard two seconds as inadequate, and recommend a three - second rule . German law requires a minimum 0.9 second distance but when tested under relaxed conditions researchers found that their test subjects spent 41% of the test time at following distances under 0.9 second . </P> <P> The United States National Safety Council suggests that a three - second rule--with increases of one second per factor of driving difficulty--is more appropriate . Factors that make driving more difficult include poor lighting conditions (dawn and dusk are the most common); inclement weather (ice, rain, snow, fog, etc .), adverse traffic mix (heavy vehicles, slow vehicles, impaired drivers, pedestrians, bicyclists, etc .), and personal condition (fatigue, sleepiness, drug - related loss of response time, distracting thoughts, etc .). For example, a fatigued driver piloting a car in rainy weather at dusk would do well to observe a six - second following distance, rather than the basic three - second gap . </P>

It is best to increase your following distance to three seconds when