Presignal Used to Increase Bus- and Car-Carrying Capacity at Intersections: Theory and Experiment

In theory midblock presignals can be used to increase the capacity of signalized intersections [The authors define “presignal” as “a set of signal heads that are installed in the middle of a block upstream of an intersection.”—Ed.]. The capacity is increased because presignals can reorganize how traffic is stored between a presignal and an intersection downstream. However, different vehicle classes have different acceleration characteristics, and the effectiveness of presignals hinges on the assumption of linear superposition; that is, the total time to discharge a mixture of distinct vehicle classes equals the sum of the times to discharge each vehicle class separately. This assumption has not been tested in the field. In this study, results from a natural experiment are used to validate the assumption for the case of cars and buses. The effectiveness of presignals to increase intersection capacity is also demonstrated.