Mixed signals: Uptick in crashes follows yellow-arrow upgrades

Traffic signal upgrades intended to smooth traffic and improve safety appear to have slightly increased crashes in Sioux Falls.

The city has installed flashing yellow left turn arrows at 30 intersections since 2010. The lights signal permission to drivers to turn left after yielding to oncoming traffic and pedestrians.

The flashing arrows are encouraged by the federal government based on safety studies, but an Argus Leader Media analysis shows crashes were more common at almost half of the intersections after the signals were installed.

A review of crash data at 18 intersections where flashing yellow turn arrows were added to existing traffic signals showed a 7 percent overall increase in accident rates. A few intersections saw crash rates decrease while others saw sharper increases.

City traffic engineers hope the numbers merely reflect a learning curve, but others think the blinking arrows are sending mixed signals to drivers.

“They think they have to rush through," said Ray Wiener, who's witnessed the confusion from his home just off Russell Street and Western Avenue.

Crash frequency at that intersection doubled after yellow turn arrows were installed in August 2014, but the change also coincided with the opening of the nearby Denny Sanford Premier Center.

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Other intersections that experienced significant increases in crash frequency after flashing yellow turn arrows were installed include East 8th Street and Cliff Avenue, East 41st Street and Veteran's Parkway, and East 54th Street and Cliff Avenue.

Accident frequency went down at 10 of the 18 intersections. That's what traffic engineers expect from the signals, which are intended to more specifically communicate right-of-way to drivers than a solid green signal with no turn arrow.

The first flashing yellow turn arrows in Sioux Falls went up at 60th Street North and Marion Road in 2010. Federal Highway Administration studies have shown drivers are more cautious when facing a flashing yellow turn arrow compared to a solid green light.

It's hard to say why crash rates went up at certain intersections, but there are lots of potential variables besides the yellow arrows, said Heath Hoftiezer, City Hall's principal engineer. The crash data could reflect more traffic or faster speeds, for example.

Or, drivers may just need more time to get used to the signals.

“There’s a learning curve every time we switch one of these out,” Hoftiezer said.

Other cities have added signs alongside the flashing arrows to remind drivers they need to yield to oncoming traffic. Hoftiezer's department has opted against that because they don't want to overload drivers with too much information.

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Most intersections with designated turn lanes will likely have them eventually, Hoftiezer said. But with a cost of up to $10,000 a light to make the switch, that’s a long way out, enough time for drivers to get used to them.

It's too late for Dan Farris. The customized front end of his 2006 Ford Mustang was taken out in August 2015 by a driver turning through a flashing yellow arrow. 

A police accident report list the left turn as a factor.

Or as Farris says: "that damn yellow light."