The City of Round Rock plans to soon implement a new traffic signal display meant to provide a safer and more efficient left turn for drivers, city staff said at the Jan. 12 City Council meeting.

A flashing yellow arrow (FYA) left turn signal will replace the circular green indication for left turns at selected intersections. The flashing arrow will allow drivers to make a left turn when oncoming traffic is clear.

The implementation is a result of national signal system changes made to the 2009 Manual on Uniform Traffic Control Devices (MUTCD) made effective Jan. 15, 2010. States were given a two-year period from the effective date to either adopt the MUTCD or have a State MUTCD/supplement that is in substantial conformance with the National Manual.

Texas adopted a State MUTCD on Dec. 8, 2011, prompting cities to begin the implementation of the new system if they have not already done so.

Round Rock Transportation Director Chad Wood said the purpose of the flashing yellow arrow is to solve the left-turn trap problem, dubbed the "amber tramp." The trap, he explained, occurs when a left-turning driver coming from the direction that received the yellow and red signal thinks that both directions of traffic got a yellow light at the same time. The driver believes opposing cars will stop and makes a turn across traffic that still has a green light, thus causing an accident.

"It's going to reduce 30 [precent] to 40 percent of amber trap-type accidents," Wood said.

When the new system is implemented:

• A solid red arrow means drivers turning left must stop.
• A solid yellow arrow indicates the traffic signal will be turning red. Drivers should not assume oncoming traffic has a red light, as their signal may still be green.
• A flashing yellow arrow means turns are allowed, but drivers must first yield to oncoming traffic and pedestrians, then proceed with caution.
• A solid green arrow means drivers should turn left and oncoming traffic must stop.

Wood said the flashing yellow arrows will be installed at all new signal projects and that existing wiring will be reused during installation. In addition, he said only existing five-section signal heads will be replaced with new 4-section signal heads for flashing yellow arrows.

Wood told council members the conversion will cost about $7,000 per intersection for an estimated total of $140,000.

Wood said the city had been waiting to hear from the Texas Department of Transportation for the last 18 months as to when the state would adopt the changes. He said the city had been led to believe that the changes would not be adopted until later in 2012, not in December 2011.

Wood said San Antonio, Waco and Houston have already begun using flashing yellow arrows as part of their traffic signaling systems.