Analysis of network exit functions for various urban grid network configurations

Macroscopic networkwide traffic models have been used to study aggregate traffic behavior on urban networks and to design traffic control strategies. However, less attention has been given to their application in the study of street network design. This paper uses the network exit function (NEF) to analyze traffic performance on an abstract grid network of various street configurations. The NEF is an aggregate relationship between trip completion rate and the number of vehicles circulating in a network. Street configuration is a topic of interest in many cities, especially in the United States, where city planners are considering street network conversions. Three configurations are addressed here: two-way streets, two-way streets with prohibited left turns (TWL), and one-way streets. This work builds on previous studies by incorporating more realistic traffic dynamics with microsimulation software (VISSIM) with dynamic traffic assignment enabled to emulate better the behavior of real drivers. This work finds that NEFs of two-way networks generally are smaller than those of TWL and one-way networks because of reduced capacity at intersections. Comparison of TWL and one-way networks is more nuanced, as traffic performance on these networks depends on route choice. If vehicles are always routed through the path with the shortest travel time, TWL networks offer NEFs with higher trip completion rates; however, if vehicles spread themselves across multiple alternatives, one-way networks provide better results. TWL networks offer a better trade-off between distance traveled and capacity at intersections, and one-way networks offer more shortest-path routing choices between origin-destination pairs.