News & Press Releases

Tuesday, February 09, 2010
New left-turn signal expected to improve safety, reduce traffic delays for drivers

Motorists on State Street will notice something new – flashing yellow, left-turn arrows that will make navigating intersections safer and easier.

The Ada County Highway District (ACHD) installed the first of several signals with flashing yellow, left-turn arrows. The new signal head at State Street/Bloom Drive/Plantation River Drive replaces the traditional green ball with a flashing arrow to tell drivers that they can turn left if it is safe to do so with no oncoming traffic (please see attached graphic). Both the yellow arrow and green ball indicators reduce traffic delays, but research has shown the arrows reduce accidents.

“The flashing yellow arrow is more clearly understood, which helps make it a safer signal,” said ACHD Traffic Engineering Supervisor Ross Oyen. “The solid green sends a message of ‘I can go’ versus a yellow arrow that sends the message that ‘I better be cautious.’”

The first of several arrow signals was installed at State/Bloom/Plantation on Tuesday morning. The second is expected to go in at State/Market Place Lane on February 18, 2010. Arrow-signals will also be installed at State Street’s intersections with Willow Lane, Ellens Ferry Drive, Collister Drive and possibly Pierce Park Lane in coming weeks.
If the new signals perform as expected, increasing safety while reducing delay, ACHD will install the flashing arrows throughout the county. In late 2009, the federal government approved the signals for wide use after several years of testing.

As a countywide highway district, ACHD manages all of the traffic signals in Ada County, even those on state highways. For more information about the new flashing arrow signals or the District, visit

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