http://www.slate.com/id/2232555/

Enter the Idaho stop-sign law. The rule, passed by the Idaho state
legislature in 1982 and updated in 2005, essentially allows bikers to treat stop
signs as yield signs. If a biker slows down and sees no cars coming, he or she
can roll through a stop sign—a so-called "rolling stop." The "Idaho
stop" has become a rallying point for vehicularists and facilitators alike—a
sort of Great Compromise for bicycles. Many vehicularists like it, because it
acknowledges the proper role of bikes on the street rather than on silly
pathways (although purists will say that it should apply to cars as well).
Facilitators like it because it recognizes a core difference between cars and
bikes: the importance of momentum. As
this great video explains, riding a bicycle becomes a lot less efficient as
soon as you have to start making regular, complete stops.