New signal control strategy for isolated intersections
CTS Research E-News, August 2009
Rural and suburban intersections can benefit from improved traffic signal control.
Smoothing out traffic flow through isolated rural and suburban high-speed intersections is the latest traffic management challenge taken up by researchers in the University of Minnesota’s Department of Civil Engineering. Assistant professor Henry Liu and graduate student Sundeep Bhimireddy developed a traffic signal control strategy that reduces traffic flow disruption occurring when groups of vehicles traveling at highway speeds are forced to stop frequently at isolated intersections. The research was funded by the Minnesota Department of Transportation.
According to the final research report, most of the rural or suburban high-speed isolated intersections have higher traffic volumes on the major approach compared to the minor approach. Often, these intersections are not close enough to one another to provide coordination and not far enough to disperse vehicle platoons completely on the major approach. These vehicle platoons on the major approach are forced to stop frequently due to conflicting calls placed by few vehicles on the minor approach. As a result, these intersections operate poorly, especially during peak periods.
In addition, advance warning flashers are used at these intersections to provide advance warning of end of green to the motorists. The conventional method uses a technique known as “trailing overlap green” that holds the green for a fixed time after gap-out. This trailing overlap green replaces the existing dilemma-zone protection provided by loop detectors installed near the intersection, and also increases delay on the minor approach.
Liu and Bhimireddy developed an integrated system that provides both platoon progression and advance warning of end of green and evaluated its performance in terms of delay, stops, and advance warning time. Cabinet-in the-loop tests were performed using a real-world scenario. These study results showed a 50 percent reduction in delay and stops on the major approach with platoons, and total intersection delay and stops were reduced by as much as 20 percent. The system was also successful in providing advance warning to the motorists by predicting gap-outs 7 to 8 seconds earlier in the majority of the cases.
Development of a Platoon-Priority Control Strategy with/out Smart Advance Warning Flashers for Isolated Intersections with High-Speed Approaches (Mn/DOT 2009-23) is available from the ITS Institute Web site.