Real-time traffic control policy for oversaturated arterials

When traffic demand routinely exceeds intersection capacity along an arterial system, existing signal control policies (even queue sensitive ones) fail to adequately address the resulting growth of queue lengths over successive signal cycles. These growing unstable queues lead to intersection spillback, intersection blockage, and the consequent spread of congestion.; A better approach is a control policy that “switches objectives” when oversaturation is detected to enforce the explicit conditions that intersections should not be blocked by queue growth, nor starved for vehicles to process. The control objectives for this policy are: (1) maximize system throughput, (2) fully utilize link storage capacity, and (3) provide equitable service. For the control of undersaturated arterial links, the conventional “progressive movements, minimize delay” objectives are included as part of this control policy.; This new control policy was first introduced in the research project NCHRP 3-38(3)[3] and called “IMP (Internal Metering Policy)” or “IMPOST (Internal Metering Policy to Optimize Signal Timing”). A MILP (Mixed-Integer Linear Programming) was formulated as the product of this research, which provides optimal values of control parameters for the mix of congested and non-congested approaches.; Subsequent work[4] extended these algorithms to apply the policy to a real-time traffic environment. This study showed that IMPOST can provide significantly improved service in terms of total delay and speed during congested conditions compared with other fixed control policies, PASSSER and TRANSYT. However, this study did not fully implement IMPOST for real time application, missing required features such as signal transition, on-line calculation of MILP, and queue length estimation, etc.; This subsequent research of these two previous works formulated a R&barbelow;eal T&barbelow;ime I&barbelow;nternal M&barbelow;etering P&barbelow;olicy to O&barbelow;ptimize S&barbelow;ignal T&barbelow;iming (aptly named RT/IMPOST). Real-time software was developed to test the control policy in a real-time simulation environment. All the missing features in the previous work required for real time application were added and are described in detail throughout this dissertation. Comparison with other fixed control policies was conducted for a test arterial.