Projects
Optimization of Dynamic Red-Light-Hold System
for Detection and Treatment of Red-Light Running
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Overview:
Red-light running (RLR) is a serious problem in the United States. As traffic volumes continue to increase, locations that were once two-way stop controlled intersections become signalized and signalized intersections operate under longer cycle lengths and redistributed green time to accommodate increasing traffic. The net result of these changes is greater intersection delay forcing hurried drivers to “make up” for their delay, leading to a greater occurrence of red-light running.
RLR events vary widely in driver intent, safety implications, and appropriate countermeasures. In general, RLR events can be broken down into two general categories: avoidable and unavoidable. Avoidable RLR incidents occur when a driver believes that is possible to safely stop, but intentionally runs the red light anyways. Avoidable RLR events typically occur very soon after the onset of the red indication. Unavoidable RLR incidents are those where drivers either 1.) believe they are incapable of stopping and thus intentionally run the red light or 2.) are unaware of the need to stop and unintentionally run the red light.
Intentional RLR events typically occur very early into the red indication and are the most common type of event, although they only account for approximately 20 percent of the RLR-related crashes, the most common of which are left-turn opposed crashes. Unintentionally RLR events are much less common and often occur well-after the onset of the red indication. Unintentional RLR events typically have much more serious implications since they account for approximately 80 percent of the RLR-related crashes, the most common of which are right-angle crashes.
Fortunately, a low percentage of RLR events actually result in crashes. However, RLR is still a rapidly increasing problem across the United States and countermeasures are necessary. There are two general categories for countermeasures to the RLR problem: enforcement and engineering. Modifications to the traffic signal operation are some of the most widely used engineering countermeasures to treat RLR. Addition of an all-red clearance interval is a common first-step to prevent RLR conflicts. Some researchers have found that increasing the yellow interval duration by 1.0 second (interval not to exceed 5.5 seconds) is correlated with a decreasing frequency of red-light violations by at least 50 percent and is especially effective at locations where the yellow time is shorter than that recommended by ITE.
Dynamic phase-by-phase extension of the green- yellow- or all-red-interval has great potential for reducing RLR events, although accurate advanced detection is required. Recent advancements in machine-vision and radar detection systems for intersection operation have made it possible to accurately detect and predict RLR events based on speed and distance of vehicles from the intersection. The research that is described here will focus on evaluation of technology designed to detect, predict, and treat RLR events through the dynamic extension of the all-red clearance phase.
The City of Milwaukee is considering the use of a red light running safety countermeasure at up to 40 intersections. The proposed concept will provide an advanced traffic signal system designed to reduce the crash risk due to red-light-running by holding the all-red phase of the signal cycle upon detection of a potential red-light runner. The system under consideration is manufactured by Optisoft. Potential red-light-runners are detected by a red-light-hold (RLH) processing unit which instantaneously analyzes the speed and distance information obtained from a radar sensor unit mounted to the signal pole. Speed and distance information is measured and fed to the RLH unit every 0.2 seconds. An all-red hold call is placed to the signal controller only if the RLH unit determines that an oncoming vehicle cannot stop in time to safely clear the intersection within a predetermined time frame. The system is capable of providing enforcement-support through transmission of red-light running information (i.e., phase status, how long after red, maximum speed) to the PDA of a nearby police officer.
A multi-year evaluation of the Milwaukee installations is proposed and will include both a safety and operational analysis. Measures of the safety effectiveness will include the number of vehicles running red, number of vehicles in or entering the intersection when conflicting phase is green, number of vehicle-vehicle conflicts, and a comprehensive statistical analysis of crashes (i.e., safety). Initial evaluation of the RLH system will focus on optimization of the system operations. Tasks of the initial evaluation will include determination of: operating parameters, operational impacts, optimization algorithm, enforcement needs, and legal issues.
One of the first tasks that will be accomplished is determination of the operating parameters for the RLH system, including: definition and characteristics of target red-light runners, appropriate maximum deceleration rate, and exclusion of non-target vehicles or false calls, such as right and left-turning vehicles, and determination of the characteristics/traits that would make the RLH system appropriate for installation at an intersection. Because any extension of the all-red phase will change the timing of other phases, it will be important to determination of the operational impacts of the system, including: cycle recovery after a RLH extension, impact of RLH extensions on a coordinated signal network, and how to best return a network to normal operation after a RLH extension.
The culminating effort of the operational analysis will be development of an algorithm that optimizes the RLH decision-making process. In other words, given the conditions of all vehicles on the approach and the signal timing, what variables should be considered and in what range to trigger a RLH extension. Determination of the need for enforcement support will be based on the extent of intentional driver abuse the RLH system as drivers become more familiar with its operation. At this time, no plans exist for automated enforcement support since such systems are prohibited by Wisconsin state law. Finally, the initial evaluation will include determination of potential legal issues, such as liability of maintaining variable all-red intervals that are outside the guidance of the MUTCD and ITE and corresponding modifications that must be made to include variable all-red intervals.
Documents:
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