  Urban transportation is a complex phenomenon. Since many agents are
constantly interacting in parallel, it is difficult to predict the future state
of a transportation system. Because of this, optimization techniques tend to
give obsolete solutions, as the problem changes before it can be optimized. An
alternative lies in seeking adaptive solutions. This adaptation can be achieved
with self-organization. In a self-organizing transportation system, the
elements of the system follow local rules to achieve a global solution. Like
this, when the problem changes the system can adapt by itself to the new
configuration.
  In this chapter, I will review recent, current, and future work on
self-organizing transportation systems. Self-organizing traffic lights have
proven to improve traffic flow considerably over traditional methods. In public
transportation systems, simple rules are being explored to prevent the "equal
headway instability" phenomenon. The methods we have used can be also applied
to other urban transportation systems and their generality is discussed.
