Two-second rule 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. 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
Two-man rule of the two-man rule to secure large sums of money and valuable items. Under this concept, unlocking the vault requires two individuals with different keys if the vault is secured by a key lock system. For bank vaults secured by combination lock, one individual will know half of the combination and a second person will know the remaining half. At no point will either person know the other person's half of the lock combination, requiring both persons to be physically present in order to unlock the vault. As an extension of the broader rationale for the "two-man rule", regulations for