The survivable weather-responsive traffic signal system developed as part of this project was evaluated and tested by conducting two analyses: traffic system benefits analysis and software testing and risk analysis. The potential crash reduction benefits, expressed as the percent reduction in total, rear-end, and crossing conflicts, are highest during snowy and icy weather conditions.

The weather-responsive system developed in this project has five innovations:

• The system operates and achieves its potential using current traffic controller and controller cabinet technologies
• The system is compatible with future applications within the FHWA's connected-vehicle initiative
• Minimal hardware, in addition to traffic controllers, is required for full system implementation
• Computer driven algorithms implement traffic signal control decisions using Clarus data
• The proposed system architecture employs two revolutionary software design approaches: design for survivability and software performance measurement at the task level.

Furthermore, the software design incorporates self-diagnostic techniques for fault detection and recovery to maximize the survivability and the security of the system. Because the proposed system has very similar computational requirements to other field traffic control applications, it serves as a major milestone in the development of secure and dependable real-time traffic control systems.

Researchers recommend that future research focused in the following three areas would be also beneficial:

• Field testing the system at signalized intersections in a variety of weather conditions
• Expanding control modifications to include other traffic control parameters, such as passage time, minimum green, and offsets
• Increasing the power of the system to maintain reliable, secure, and survivable traffic signal service.

FINDINGS

The potential crash reduction benefits increase as the traffic volume level increases.

• Rear-end conflicts are the conflict type projected to be most eliminated by a weather-responsive traffic signal system with a potential average reduction of approximately 22 percent for moderate volume levels and 43 percent for high volume levels.
• The weather-responsive signal timing plans also show considerable potential in reducing traffic delays and stops.
• The percent reduction increases as the traffic volume level increases. The potential reduction in delays and stops seems consistent with what has been reported in the literature.

The reduction in average speeds and saturation flow rates, and the increase in start-up delays, make normal signal timing parameters unsuitable during inclement weather. In addition, with reduced pavement friction and visibility, default all-red and amber clearance intervals become unsafe as motorists are more likely to be trapped in dilemma zones at the onset of red. Several studies have investigated the effect of inclement weather on various signal timing traffic parameters. Studies have shown that weather-responsive signal timing plans can improve both the safety and efficiency of the traffic signal system operations.

• Simulation studies revealed benefits of approximately 7 percent to 23 percent reduction in average delay, 4 percent to 9 percent reduction in vehicle stops, and 3 percent to 12 percent increase in average speeds.

This report, finalized in December 2011, is an assessment of research focusing on Integrating Clarus Data in Traffic Signal System Operations for safety and mobility. These findings along with the benefits provide a valuable resource to those considering the implementation of weather responsive traffic management systems.