Wavetronixby Don Leavitt, Wavetronix LLC
The dreaded intersection 'dilemma zone' is under the spotlight—can safety improvements be made?
Intersection control is a primary concern of traffic management professionals around the world. As urban and suburban populations grow, the challenges of effectively managing intersection traffic flow increase. Many traffic professionals are discovering the benefits of advanced warning systems that notify drivers of the changing light as they approach an intersection. A study of such systems in Utah is using the Wavetronix SmartSensor Advance™ to determine their effectiveness in providing both safety and efficiency to intersection control situations.
Intersections are particularly difficult to manage because of the high volume of vehicles traveling in different directions. The potential for accidents is great, even at signal-controlled intersections, particularly in the area near the intersection known as the “dilemma zone.” Dilemma zones, or decision zones, are where a driver, when faced with a yellow warning light, must decide whether to stop suddenly or proceed through the intersection and try to “beat” the red light. If the driver chooses to stop for the light, he faces the possibility of a rear-end accident with the vehicle behind him; if he chooses to proceed, he risks running the red light and being involved in an angle or side-on accident. These risks increase at high-speed intersections where the speed of vehicles through the intersection is greater than 35 miles per hour.
In the United States, intersection dangers are well illustrated by national crash statistics. According to the National Highway Traffic Safety Administration's Traffic Safety Facts, the U.S. had more than 6.3 million police-reported motor vehicle accidents in 2003; 2.56 million, or more than one-third, of those accidents occurred at, or near, an intersection. Of the intersection-related accidents, more than 8,600 of them involved a fatality, accounting for nearly 25 percent of the fatal crashes that occurred.
According to a University of Cincinnati study of dilemma zones in Ohio, the goal of signal-controlled intersections is to provide safe driving conditions without sacrificing efficiency. The study noted that many traffic engineers are forced to choose between safety and efficiency, especially when signal-controlled intersections are located within 2,000 feet of each other (Dilemma Zone Protection and Signal Coordination at Closely-Spaced High-Speed Intersections, University of Cincinnati, November 2001).
Advanced intersection warning systems (AWS) attempt to bridge this gap between safety and efficiency. They alert drivers that the traffic signal has changed from green to yellow before they reach the intersection, and traffic engineers hope this advanced warning will reduce intersection crash rates and red light violations by increasing driver reaction time.
The Utah Department of Transportation is implementing an advanced system that uses video devices to monitor traffic as it passes a point approximately 750 feet away from the next signal-controlled intersection. When the signal light changes to yellow, the signal controller triggers a dynamic message board, located approximately 450 feet from the intersection, to display the message “Prepare to Stop” for motorists approaching that intersection. The system is being tested at three separate locations on a 23.5 mile long, limited-access expressway that runs along the western side of Salt Lake City. UDOT officials hope the system will reduce red light running and accidents at intersections by notifying drivers of the changing light well before they reach the intersection dilemma zone.
Engineers from Brigham Young University (Provo, Utah) are studying the effectiveness of UDOT's advance warning system and they are using the SmartSensor Advance to collect the data needed for the study. Grant Schultz, Ph.D., PE, PTOE, an assistant professor in BYU's Department of Civil and Environmental Engineering, is installing SmartSensor Advance devices at the dynamic message boards, facing toward the intersection to monitor the speed of vehicles as they approach the signal. SmartSensor Advance will also be used to determine whether or not the system effectively reduces the number of vehicles passing through the intersection after the red light.
The Wavetronix SmartSensor Advance is a radar detection device specifically designed for intersection and dilemma zone management. Like the original SmartSensor, SmartSensor Advance uses patented Digital Wave Radar™ technology to measure vehicle presence and speed in up to eight detection zones, at a range of 500 feet. With twice the detection range of video monitoring systems, SmartSensor Advance provides traffic operation officials with effective dilemma zone management, system efficiency control of traffic signals and presence detection of vehicles.
“SmartSensor Advance is an excellent alternative for speed and vehicle detection,” says Dr. Schultz. “It is flexible, so detection zones can be adjusted to meet the needs of the study, and it's portable, so the study can be moved from intersection to intersection, thus increasing the amount of data collected.”
The information gathered by SmartSensor Advance will be delivered to a data logging device via Wavetronix Click!™ wireless communications. Although the SmartSensor Advance is designed for dilemma zone management, it is not part of UDOT's advance warning system, but it is an important part of the study to see how effective the AWS will be. New AWS installations will be able to use the SmartSensor Advance as the monitoring device for intersection control. For more information about SmartSensor Advance, Click! or Wavetronix, visit www.wavetronix.com.