As an example for the optimization of unstable flows, we present an economi
cs-based method for deciding the optimal rates at which vehicles are allowe
d to enter a highway. It exploits the naturally occurring fluctuations of t
raffic flow and is flexible enough to adapt in real time to the transient f
low characteristics of road traffic. Simulations based on realistic paramet
er values show that, this strategy is feasible for naturally occurring traf
fic, and that even far from optimality, injection policies can improve traf
fic flow. Moreover, the same method can be applied to the optimization of f
lows of gases and granular media.