Q. Why does the stoplight at South 17th intersection at John D. Barry/St. Andrews Drive not keep the left turn-only light working at all times, since it is so dangerous turning left off of 17th onto John D. Barry?”
A. The left-turn signal at the intersection of South 17th Street and John D. Barry/St. Andrews Drive is activated via detectors in the road.
Denyz Vielkanowitz, the city of Wilmington’s signal systems management engineer, said a vehicle needs to be stopped behind the stop bar to trigger the left-turn arrow.
“Common driver tendencies is to creep forward while waiting to (turn),” Vielkanowitz said. “ In doing so, the vehicle creeps out of the detection zone and the traffic signal does not recognize its presence anymore or the need to display the left turn arrow. This is by far the No. 1 complaint received and is usually addressed to the satisfaction of the citizen once the information is distributed. “
Furthermore, a car trying to make the turn needs to be stopped over the detector for at least 10 seconds. That delay is designed to keep the light from cycling through the green turn arrow if a car approaches the intersection and legally makes the turn.
“This 10 second delay programming feature is typical for this type of traffic signal design,” Vielkanowitz said. “ If the vehicle stops behind the stopbar for the programmed delay time and once traffic has cleared in the opposing directions appropriately, the traffic signal will progress to the left turn arrow as designed.”
Traffic traveling in opposing directions is picked up at some intersections using stopbar detectors and at others using sensors approaching the stopbar. The traffic signal system bases its signal changes on the specific directions of travel and applies the necessary timing to get vehicles through the intersection before moving on to the next signal.
Date posted: July 2, 2013
User-contributed question by: