The Spatial Variability of Vehicle Densities as Determinant of Urban Network Capacity

CCSS Working Paper Series, CCSS-09-009

Amin Mazloumian, Nikolas Geroliminis, and Dirk Helbing

“Due to the complexity of the traffic flow dynamics in urban road networks, most quantitative descriptions of city traffic so far have been based on computer simulations. This contribution pursues a macroscopic (fluid-dynamic) simulation approach, which facilitates a simple simulation of congestion spreading in cities. First, we show that a quantization of the macroscopic turning flows into units of single vehicles is necessary to obtain realistic fluctuations in the traffic variables, and how this can be implemented in a fluid-dynamic model. Then, we propose a new method to simulate destination flows without the requirement of individual route assignments. Combining both methods allows us to study a variety of different simulation scenarios. These reveal fundamental relationships between the average flow, the average density and the variability of the vehicle densities. Considering the inhomogeneity of traffic as an independent variable can eliminate the scattering of congested flow measurements. The variability also turns out to be a key variable of urban traffic performance. Our results can be explained through the number of full links of the road network, and approximated by a simple analytical formula.”

Inference from Spatiotemporal Pattern and Digital Representation of Embedded Networks

Spatio-Temporal Constraints on Social Networks Workshop, University of California, Santa Barbara, Center for Spatial Studies, 13-14 December 2010

Michael Goodchild

“The position papers submitted for the meeting raise a fascinating array of issues, ranging from representation and analysis to the social context. I would like to focus on two issues that seem to me not to have received much attention in the papers, but to be important in addressing the topic of the meeting.”