Increasing the Flow Capacity of Signalized Intersections with Pre-signals: Theory and Case Study

The dissertation proposes a new "tandem design" to reorganize traffic and increase the flow capacity of signalized intersections. In the tandem design, a mid-block pre-signal is used to sort left-turning vehicles (LVs) and through-moving vehicles (TVs) in tandem, rather than leaving them side by side, as in the conventional design. For intersections with separate through and left-turn phases, the tandem design outperforms the conventional one because more lanes can be used to discharge traffic during at least one of the intersection signal phases. We find that the tandem design can increase the intersection capacity by 10% to 20% in its simplest form. We also study the length requirement of blocks to fully realize the capacity benefit, and modifications of the tandem design to reduce this length requirement. We then conduct a case study at a signalized intersection in the city of Chengdu, China. The case study shows that the tandem design can effectively increase intersection capacity. Moreover, the case study shows that together with enforcement of the bus-lane restriction, both cars and buses can benefit. Finally, we demonstrate how the idea of tandem sorting with pre-signals can be extended to increase intersection capacity of multimodal traffic, using as an example the case of cars and buses. This extension hinges on an assumption that the discharge times of different modes of transport is additive, and this assumption is confirmed with a natural experiment