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Summer 2011

Signs use solar power to make rural intersections safer

A TechFest attendee maneuvers a Scout reconnaissance robot. photo: Matt Miranda

As they approach the Duluth intersection where the system is installed, northbound and southbound drivers on the minor road see the message “Vehicle approaching when flashing.”

In Minnesota, most intersection-related crashes occur at rural, two-way-stop intersections because drivers stopped on a minor road often cannot see traffic on the major road. Nearby vertical and horizontal curves increase the risk when entering the intersection. At these intersections, right-angle crashes account for the largest percentage of crashes, and most are related to drivers’ inability to recognize a safe gap in the traffic stream.

To improve safety at these rural, two-way-stop intersections, researchers from the University of Minnesota Duluth, working with St. Louis County, Minnesota, developed the ALERT System (Advanced LED Warning Signs for Rural IntersecTions Powered by Renewable Energy). Sponsored by the Minnesota Local Road Research Board, this low-cost, dynamic warning system provides traffic information to drivers approaching the intersection.

Vehicle detectors placed at each approach send messages to LED blinker signs. The system is wireless and powered by solar panels, which eliminates problems associated with buried wires as well as the need to connect to a local power grid.

The system was installed at the intersection of West Tischer Road and Eagle Lake Road in Duluth. This intersection has a severe vertical curve on the east approach of the major road that significantly reduces sightlines for drivers stopped on the north and south approaches of the minor road. In addition, westbound drivers on the major road cannot see cross traffic until they are nearly in the intersection.

Westbound drivers see the message “CROSS TRAFFIC WHEN FLASHING.” North and southbound drivers on the minor road see the message “VEHICLE APPROACHING WHEN FLASHING.”

The research team included Taek Kwon, a professor in the Department of Electrical and Computer Engineering; research associate Ryan Weidermann; and St. Louis County traffic engineer Victor Lund.

According to Lund, ALERT was “tremendously successful” at changing driver behavior. When the alert signs were flashing, westbound traffic on the major road slowed 4 mph, drivers on the minor road waited longer before crossing, and roll-throughs were eliminated.

However, when the alert sign was not flashing, drivers on the minor road apparently assumed there was no cross traffic. As a result, they did not always obey the stop sign, and roll-throughs increased, Lund says. This increases the risk of crashes when the device stops working—as ALERT did on several sunless days last winter.

Driver-assistance devices for intersections, such as ALERT, are effective, Lund says. But he adds that standardization is needed before these devices can be widely used. This means that state and federal standards must be established for messaging, illumination, and placement of signs. Fail-safe issues—such as malfunctioning solar panels — must also be dealt with.

Ease of maintenance is also an issue. Lund notes that county employees currently need to climb a ladder to service ALERT, but he’s hopeful that one day all components will be enclosed in a ground-level service cabinet, which would eliminate the need for a ladder and allow for easier access.