  We present a fluid-dynamic model for the simulation of urban traffic networks
with road sections of different lengths and capacities. The model allows one to
efficiently simulate the transitions between free and congested traffic, taking
into account congestion-responsive traffic assignment and adaptive traffic
control. We observe dynamic traffic patterns which significantly depend on the
respective network topology. Synchronization is only one interesting example
and implies the emergence of green waves. In this connection, we will discuss
adaptive strategies of traffic light control which can considerably improve
throughputs and travel times, using self-organization principles based on local
interactions between vehicles and traffic lights. Similar adaptive control
principles can be applied to other queueing networks such as production
systems. In fact, we suggest to turn push operation of traffic systems into
pull operation: By removing vehicles as fast as possible from the network,
queuing effects can be most efficiently avoided. The proposed control concept
can utilize the cheap sensor technologies available in the future and leads to
reasonable operation modes. It is flexible, adaptive, robust, and decentralized
rather than based on precalculated signal plans and a vulnerable traffic
control center.
