The Uncertainty of Delays at Optimal Pre-timed and Vehicle Actuated Signals

Although extensive research has been carried out in the past to assess the performance of control signals under different service mechanisms, little interest has been given to the way these control methods deal with the variability of traffic. This paper proposes a probabilistic approach to calculate delay and queue length distributions in time. This method has been used to compare the effects of simple pre-phased controls based on delay minimization and of vehicle actuated controls, which look at the actual headway distribution of vehicles without looking explicitly at vehicle delays. This study confirms the superiority of gap-based mechanisms over delay-based controls also in terms of delay variability, given their property to adapt green and cycle lengths according to the real amount of traffic arriving during each cycle.