Friday, November 30, 2012
Allen swaps in flashing yellow arrows at protected left turn lights
Drivers apparently don't already know to yield to oncoming traffic...
Allen They're easier to understand. They're safer. They're flashy.
They're flashing yellow arrows (FYAs), and the city of Allen has joined other North Texas cities - including McKinney, Plano and Richardson - in installing the signals at selected intersections where protected left turns exist.
The installations follow recommendations found in a study conducted for the U.S. Department of Transportation's Federal Highway Administration showing the FYAs help reduce crashes and wait times in intersections and allow engineers to program signal timing to respond to traffic volume.
"The flashing yellow will take the place of the solid green ball," said Shawn Poe, assistant director in the city's Engineering and Traffic division. "The flashing yellow is to alert the driver to oncoming traffic before making a left turn."
Flashing yellow arrows are being phased in as new construction or modifications to existing signals are necessary and as funds allow.
"The only one we're doing at this time, that we've got plans for, is the one at Cheyenne and Bethany," Poe said. "We had to do some signal modifications for the Bethany road expansion.
"The funding comes from the capital improvement plan," he said. "On Bethany we had county funds also. There are no grants at this time.
"The cities of Frisco and McKinney have already implemented flashing yellows at some intersections," Poe said. "Other area cities are in the process; I know I've seen some in Arlington as well.
"This comes from a long national study - over 10 years long - by the Federal Highway Administration [FHWA]," Poe said. "They found there were fewer crashes with the flashing yellow rather than the solid green ball."
According to the study conducted by the National Cooperative Highway Research Program (NCHRP) for the FHWA, "the FYA was found to be the best overall alternative to the circular green as the permissive signal display for a left-turn movement; FYA was found to have a high level of understanding and correct response by left-turn drivers, and a lower fail-critical rate than the circular green; and the FYA display ... is capable of being operated in any of the various modes of left-turn operation by time of day, and is easily programmed to avoid the 'yellow trap' associated with some permissive turns at the end of the circular green display."
The "yellow trap" occurs when a driver, waiting to turn left on a green light that turns yellow, assumes the oncoming traffic's signal also shows yellow - often causing the driver to make the turn, mistakenly thinking his turn is protected.
A sign placed near the signal instructing drivers how to interpret the FYAs is not necessary, according to the study, published in 2003 as NCHRP Report 493.
"Researchers found that the flashing yellow arrow display is intuitively obvious in meaning to drivers and that an explanatory sign was unnecessary," it said.
"If you're going to err on the side of caution," said Chris Flanigan, Department of Engineering director, "that's what you'd want people to do."
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