The Minnesota Department of Transportation installed Intelligent Lane Control signs with two goals in mind: to alert motorists of lane-blocking incidents to steer them away from trouble and to better manage congestion.
A new study by researchers at the University of Minnesota’s Traffic Observatory shows that drivers are heeding the messages displayed on the high-tech warning signs designed to get them to switch lanes before they reach the point where there is a stall, crash or hazard impeding traffic.
But when it comes to mitigating congestion, well, that’s another story. Motorists never caught on to the advisory speeds to get them to slow down before they encountered gridlock. The messages were such a failure that a year ago MnDOT stopped using them.
Intelligent Lane Control signs — also known as Smart Lane technology — are the black screens that hang over each lane every quarter mile on I-94 between downtown Minneapolis and downtown St. Paul and on I-35W between downtown Minneapolis and Burnsville. MnDOT uses them to display messages to get motorists to make a smooth transition to an open lane long before they reach the blockage. The purpose is to reduce secondary fender benders that are common when traffic backs up and keep traffic away from responders.
Messages are progressive. A green arrow indicates a lane is open. A “lane closed ahead” message instructs motorists to vacate the lane. Farther upstream a flashing chevron points drivers to the lane to switch to. Finally a red X indicates the lane is unusable even if the incident is not in sight.
In the study looking at the crash-prone corridor of westbound I-94 between Cedar Avenue and the entrance ramp from northbound I-35W, the signs had the intended effect on driver behavior, meaning vehicles vacated the lanes far enough in advance to minimize traffic disruption, said study coordinator John Hourdos.
Signs vs. advisory speeds
“The signs are a very good idea and provide for more direct connection with drivers,” he said. “The project showed that you only need two, at most three, signs in a row to get the desired effect.” ”
MnDOT spent $26 million on Smart Lane technology, installed on I-35W in 2009 and 2010 and on I-94 in 2012. Until last July, the agency posted advisory speeds to warn drivers slow down before hitting a bottleneck. The idea was to slow their speed so drivers were not slamming brakes at the last minute. But drivers didn’t understand the meaning behind messages posted a mile before the bottleneck, advising them to slow to speeds of 45 miles per hour and then to 30, and congestion ensued.
“If they understood, they would have slowed down and you would have good compliance,” said Brian Kary, a freeway engineer.
MnDOT is headed to the drawing board to see how to convey congestion messages more effectively. The agency could learn from the Washington State Department of Transportation. Speeds posted on Smart Lane signs on three routes in Seattle are regulatory; compliance is mandatory.
“Drivers learned that is useful information,” said WSDOT spokesman Morgan Balogh. “They know if everybody is going to have to slow down ahead.”
There, Smart Lanes have led to 7 percent fewer crashes and improved road capacity, he said.
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