Transportation

We Can do Something About the Weather: Adapt Traffic Signal Control Strategies

We can’t change the weather yet, but adapting traffic signal control strategies to account for severe weather conditions is something we can do.   A recent article in the magazine Public Roads, published by the Federal Highway Administration, presents a summary of ongoing research into the collection and use of road weather data for traffic management purposes.  The article “Managing Traffic Signals During Storms”, by Ahmed Abdel-Rahim and C.Y. David Yang, Public Roads, Nov./Dec., 2012, presents results from a study by the University of Idaho on the use of Clarus weather data to drive a traffic control algorithm that directly changes the operations of connected traffic signal controllers.    What’s exciting about this article is that it addresses traffic signal control at an individual intersection and reports promising results for both reductions in delay and conflicts (accidents).    For several years now, we have been reporting the benefits of using weather information for other transportation management purposes, such as fog and low visibility warning systems as well as snow plow and deicing decision support systems.  Now, this report is one of the first applications for direct application of weather to traffic signal control parameters.

Much of the rationale for modifying traffic signal operations during severe weather is based on human factors.  Most people (at least the good drivers) slow down during heavy rain or snow fall.  Therefore, basic parameters for green band progression, such as the timing offset between adjacent intersections, need to be adjusted for the reduced speeds.  Longer phase durations on the main approaches may also be needed to maintain the same throughput at lower speeds, thereby reducing overall delay that would otherwise be introduced by the severe weather.

The laws of physics also drive some potential adjustments.  Slippery conditions due to wet or icy pavement requires longer stopping distances, even with slower speeds.  This may require longer yellow clearance intervals at signalized intersections.  These types of considerations during severe weather can also improve safety.

Now that there are proven technologies to adapt traffic signal control to severe weather, the time is right to pull together all of our best techniques to improve traffic signal control.  Traffic responsive and traffic adaptive control strategies, by themselves, have been proven to provide great benefits over fixed, time-of- day signal timing.  We still can’t do anything about weather, but we can forecast or predict weather with reasonable accuracy.  Private weather services, such as Schneider Electric’s MxVision WeatherSentry®, utilize road weather observations from systems such as Clarus to produce accurate severe weather and pavement forecasts for specific locations and timeframes.  Schneider Electric’s OPAC Traffic Adaptive Control algorithm can react to predicted traffic flows and change traffic signal timing in real-time.    Our SmartMobility platform can combine both severe weather traffic management and real-time adaptive traffic control strategies to create optimized flow and maximum efficiency under all conditions.

But we are not finished yet.  The Connected Vehicles Program promises even more data on traveler behavior that can, in turn, allow even more granularity in making traffic signal control decisions.  The connected vehicle on a connected road network is just like connected people in a social network.  The vehicle will tell us even more information, from the weather conditions that it senses to where its driver wants to go.   For ways to predict, respond and optimize traffic signal control, the sky (cloudy or not) is the limit.

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