Despite the importance of urban traffic flows, there are only a few
theoretical approaches to determine fundamental relationships between
macroscopic traffic variables such as the traffic density, the utilization, the
average velocity, and the travel time. In the past, empirical measurements have
primarily been described by fit curves. Here, we derive expected fundamental
relationships from a model of traffic flows at intersections, which suggest
that the recently measured fundamental diagrams for urban flows can be
systematically understood. In particular, this allows one to derive the average
travel time and the average vehicle speed as a function of the utilization
and/or the average number of delayed vehicles.Comment: For related work, see http://www.helbing.or