  We study a single-lane traffic model that is based on human driving behavior.
The outflow from a traffic jam self-organizes to a critical state of maximum
throughput. Small perturbations of the outflow far downstream create emergent
traffic jams with a power law distribution $P(t) \sim t^{-3/2}$ of lifetimes,
$t$. On varying the vehicle density in a closed system, this critical state
separates lamellar and jammed regimes, and exhibits $1/f$ noise in the power
spectrum. Using random walk arguments, in conjunction with a cascade equation,
we develop a phenomenological theory that predicts the critical exponents for
this transition and explains the self-organizing behavior. These predictions
are consistent with all of our numerical results.
