Impact of the Link Length on the Delay in Two-Way Signal Coordination

Signal coordination plays an important role in urban traffic control systems. Studying the influence of some factors such as the link length on the potential benefits of signal coordination can result in more efficient traffic control. Researchers have observed a highly fluctuating or damped sine-wave type relationship between the link length and the delay in two-way coordinated control, but a clear explanation of this relationship is still lacking. This paper presents a thorough analysis of the mechanism by which link length affects the delay in two-way coordination. The impact of the link length involves two aspects. We first derived formulas for the delay using shockwave queuing profiles that included the impact of the offsets in the two directions. We then conducted numerical experiments employing Robertson’s platoon dispersion model to incorporate the impact of platoon dispersion. By comparing the results from the derived formulas and the numerical experiments, we concluded that the periodicity is due to the mutual relation between the offsets in the two directions, whereas the attenuation is due to platoon dispersion. The findings should provide valuable insights for developing a more reasonable correlation degree model for the coordination of adjacent intersections. In addition, we found that platoon dispersion has a negligible influence on the critical link lengths at which the delay cannot be reduced by signal coordination. This means that whether or not platoon dispersion is considered, it will not affect the choice between the simultaneous and the alternative progressions to minimize the delay under a given link length, which is very meaningful in practical work.