[kbutler]

I'm curious how you've determined "most US States". I cited CA above - 3 or more, Washington wants 4 seconds above 35 mph. Florida says 4 seconds during normal weather and traffic conditions (more if hazardous). Utah does say 2 seconds. Texas wants 4 seconds above 30mph. New York said 2 seconds but "In bad weather and when following large trucks, increase the count to at least three or four seconds for additional space."

And in any case, the 2 seconds is not the "suggested follow distance" it's the legal MINIMUM. That is, "You're clearly unsafe if following at any less than this," rather than, "Close up any gaps more than this."