Traffic Shockwave Analysis at Signalized Intersections

Abstract

The relationship among flow, density, and speed represents the fundamental and most important properties in traffic flow theory. The purpose of this study is to analyze shockwaves at a signalized intersection. At such an intersection, a green light allows vehicles to move freely at their desired speeds until the signal changes to red, at which point vehicles must stop. During the red phase, vehicles queue up, the flow becomes zero, and the density reaches jam density. When the signal turns green again, the flow increases from zero to a maximum value, referred to as the dissipation state. Experimental data for shockwave analysis were obtained by observing a single-lane closure at a four-legged intersection. Traffic counts were recorded at 15-minute intervals over an hour and then converted to vehicles per hour for flow calculations; similar conversions were applied to speeds and densities. Shockwave speeds during both the accumulation state and the dissipation state were calculated using the average values from peak A.M., off-peak A.M., peak P.M., and off-peak P.M. periods of the data collection days. These calculated wave propagation speeds were compared with directly measured values obtained from the flow–density–speed relationship. Additionally, other parameters such as the maximum queue length and the dissipation time at the end of the red phase were determined, as these are also critical in traffic shockwave analysis.