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
Righthand head rule Righthand head rule In generative morphology, the "righthand head rule" is a rule of grammar that specifies that the rightmost morpheme in a morphological structure is almost always the head in certain languages. What this means is that it is the righthand element that provides the primary syntactic and/or semantic information. The projection of syntactic information from the righthand element onto the output word is known as feature percolation. The righthand head rule is considered a broadly general and universal principle of morphology. In certain other languages it is proposed that rather than a righthand head rule, a lefthand head