|Image Credit: The Coloradoan|
Flashing yellow arrows above left turn signals warn drivers to yield to oncoming traffic. These signals may be safer than the solid green circle alone, because some drivers interpret the green as permission to turn without checking for oncoming traffic. Flashing yellow lights seek to reduce the number of severe injury or fatalities caused by crashes involving left turns, sometimes referred to as approach-turn crashes. They also provide traffic engineers more flexibility to respond to different volumes of traffic.
For more information check out Alicia Stice’s article in the Coloradoan.