Signal Spotlight: Connected Snowplows Coming to Connecticut

The Connecticut Department of Transportation (CTDOT) has two projects planned for the Berlin Turnpike corridor in Newington, Connecticut to replace outdated traffic signal equipment, install an adaptive signal control system with automated traffic signal performance measures, and introduce connected vehicles (CV) to the state highway system. Between the two projects, a total of 27 signalized intersections will be upgraded.

The projects are part of the SPaT Challenge, a challenge to state and local public sector transportation infrastructure owners and operators to deploy dedicated short-range communications (DSRC) infrastructure with Signal Phasing and Timing (SPaT) broadcasts in at least one corridor or network in each of the 50 states. More information on the SPaT Challenge can be found at  https://transportationops.org/spatchallenge.

Along with installing new Advanced Traffic Control (ATC) controllers and fiber communications, the CTDOT plans to install roadside units (RSU) at each intersection to support vehicle to infrastructure (V2I) connected vehicle applications. One of the applications the CTDOT plans to implement is traffic signal priority for snowplows.

What are the benefits of snowplow priority?

When a snowplow must stop at a signalized intersection during plowing operations, this causes uneven application of snow removal chemicals and the plow blade must be raised to accelerate from a stop. Connected vehicle technologies are in their infancy, but there is hope that the technology will allow for more even application of material and reduce the time it takes to clear a road network. 

Traffic signal pre-emption for snowplows has been used with success in various jurisdictions. In St. Cloud Minnesota, for example, relative priority preemption reduced travel times for snowplows by an average of 22%.Snowplow drivers often work through the night with few breaks for meals and sleep, so getting plows off the roads faster can reduce the risks associated with drowsy driving.

What is traffic signal priority?

Traffic signal priority is a way to give priority to specific vehicles (typically transit vehicles) by altering signal timing to extend greens on identified phases, alter phase sequences, or include special phases. Unlike traffic signal pre-emption, which interrupts the normal signal cycle to accommodate special events like a fire truck responding to a call, traffic signal priority does not disrupt the coordination of green lights between adjacent intersections.

On-board units (OBUs) installed in the snowplow trucks will “talk” to the traffic signals, sending a vehicle-to-infrastructure (V2I) Signal Request Message to request priority. Once the traffic signal determines whether it can accommodate the request without impacting coordination with adjacent signals, the traffic signal will send an infrastructure to vehicle (I2V) message to inform the snowplow vehicle whether the request was accepted. Traffic signal priority typically involves adjusting the signal timing at an intersection for an approaching bus, or in this case, snowplow truck, to reduce the red time (early green or red truncation) or extend the green time (green extension).

To see how snowplow priority works, check out this animation from the Minnesota Department of Transportation and AECOM. More information on traffic signal priority can be found in the Traffic Signal Timing Manual.  

As a final note, don’t forget to register for the Coffee and Conversation special event on December 3, 2020, from 10:00 am to 11:00 am, where we’ll discuss the Berlin Turnpike Adaptive Signals Project. Joining us will be Mark Makuch, Greg Palmer, and Jay Lockaby of the CTDOT’s newly-created Traffic Signals Unit within the Division of Traffic Engineering. To register, visit https://us02web.zoom.us/meeting/register/tZwkf-2grT0pH9xAFUDsDHNI1lz7bIczV0Sm.

If you have traffic signal systems questions, please contact: Theresa Schwartz, P.E.,
P.T.O.E. – Traffic Signal Circuit Rider (860) 486-4535 or theresa.schwartz@uconn.edu.