U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
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Issues. Mobility or efficiency needs must be balanced with safety needs in the timing of traffic signals.
To increase safety at signalized intersections:
There is currently no recommended practice for traffic signal change intervals. RLR is one of the most common causes of intersection crashes. The generally accepted definition of the yellow change interval is to warn motorists that the related green movement is being terminated and that a red signal indication will be exhibited immediately thereafter. Some jurisdictions supplement the yellow interval with an all-red interval to provide additional clearance time for vehicles within the intersection.
Traffic signal timing needs to address all users’ needs, including pedestrians (and those with disabilities), bicyclists, and drivers of large trucks, transit vehicles, and emergency vehicles.
Increasing the number of phases to include protected left-turns reduces conflicts between opposing traffic movements. Protected left-turn phases significantly improve the safety for left-turn maneuvers by removing the conflicts with the opposing through vehicles.
Coordination of traffic signals along a route can generate safety benefits in two ways:
Traffic signal preemption allows emergency vehicles to disrupt a normal signal cycle in order to proceed through the intersection more safely, decreasing response times of emergency vehicles. Preemption systems can also be used for transit vehicles and for signalized intersections close to railroad at-grade crossings.
Issues. According to 2007 data from NHTSA's Fatality Analysis Reporting System, crashes caused by RLR resulted in an estimated 785 fatalities. This represents 9 percent of all intersection crashes for that year.
Speeders and red light violators share many of the same characteristics. As a group, red light violators involved in crashes are more likely than non-violators to be young (under 26), to not wear seat belts, to have invalid driver’s licenses, and to be alcohol-impaired. Speeders also tend to be young, drive newer vehicles, and have more speeding violations and other moving violations than slower drivers. They also have 60 percent more crashes. (Focus on Safety: A Practical Guide to Automated Traffic Enforcement, National Campaign to Stop Red Light Running, 2007. Washington, DC http://www.stopredlightrunning.com/pdfs/WEBONLY_Red%20Light%20Book.pdf) A 2006 study by the National Safety Council and Elsevier Ltd. found that “their speeding behavior is not likely to be controlled without vigorous, consistent enforcement, including the use of automated technology.” (Reducing red light running through longer yellow signal timing and red light camera enforcement: Results of a field investigation. Richard A. Retting , Susan A. Ferguson, Charles M. Farmer Insurance Institute for Highway Safety, 1005 North Glebe Road, Arlington, VA 22201, United States b Ferguson International LLC, 1328 Lancia Drive, McLean, VA 22102, United States. © 2007 Elsevier Ltd.)
RLR crashes are much more likely to cause an injury or a fatality than other intersection crashes. About half of the deaths in RLR crashes are pedestrians and occupants in other vehicles who are hit by the red light runners.
Issues. Intersection collision avoidance systems use both vehicle-based and infrastructure-based technologies to help drivers approaching an intersection understand the state of activities within that intersection.
Current research is focused on developing systems that can warn drivers of approaching vehicles. These systems can help with collision avoidance and selection of safe gaps in opposing traffic streams.
There are three types of collision avoidance systems:
Intersection collision warning systems use sensors to monitor traffic approaching dangerous intersections and warn vehicles of approaching cross traffic. This technology warns drivers of potential collisions with vehicles not complying with stop signs or traffic signals.
Additional research is needed to develop and test the detection and communication systems to be installed in roadside infrastructure or in vehicles. Installation of equipment in vehicles will likely take a long time to reach a significant level because equipment is unlikely to be added to existing vehicles.
More research into human factors is also needed to develop a driver-vehicle interface that effectively communicates the information on potential hazards to drivers.
Cooperation is required between vehicle manufacturers and highway agencies to provide information to drivers from roadside infrastructure.
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