That's certainly true for new construction, so I should probably qualify that I live in the northeast, where totally new roads are very rare, and almost all of

That's certainly true for new construction, so I should probably qualify that I live in the northeast, where totally new roads are very rare, and almost all of our roads evolved from much earlier thoroughfares. The reality in other parts of the country is probably much different (and informed by our experience here, where the first roads in the U.S. were constructed). In this part of the country it is indeed true to say that almost all traffic control structures were placed because a particular spot caused accidents.