  The transport of products between different suppliers or production units can
be described similarly to driven many-particle and traffic systems. We
introduce equations for the flow of goods in supply networks and the adaptation
of production speeds. Moreover, we present two examples: The case of linear
(sequential) supply chains and the case of re-entrant production. In
particular, we discuss the stability conditions, dynamic solutions, and
resonance phenomena causing the frequently observed "bullwhip effect", which is
an analogue of stop-and-go traffic. Finally, we show how to treat discrete
units and cycle times, which can be applied to the description of vehicle
queues and travel times in freeway networks.
