The Ada County Highway District is installing a safer and more efficient traffic signal at left turn lanes at certain intersections in Ada County - the flashing yellow left-turn arrow signal. The new signal has a flashing yellow arrow instead of the green ball used in traditional signals to tell drivers that they can turn left after yielding to on-coming traffic. While both types of signals reduce traffic delays, research has shown that the new turn signals reduce accidents and are more easily understood by drivers.

How they work

The new signal is made up entirely of arrows. A steady green arrow still indicates that left-turn drivers have the right-of-way. However, instead of a green ball, a flashing yellow left-turn arrow is used to tell drivers when they are permitted to turn left after yielding to oncoming traffic. A steady yellow arrow means that the left-turn signal is about to turn red, and that drivers should not enter the intersection if they can stop safely. A steady red arrow means that drivers have to stop and wait for a green or flashing yellow indication.

Steady Red Arrow - stop

Steady Yellow Arrow - prepare to stop

Flashing Yellow Arrow - turn left after yielding to on-coming traffic and pedestrians

Steady Green Arrow - left-turn drivers have the right-of-way

Click here to view a demonstration (animation provided by Kittelson & Associates).

Where will the new signals be installed?

ACHD will begin installing the new left-turn signals on State Street. State Street was chosen because ACHD wanted to apply the new signals to a corridor where daily users would become accustomed to the signals. Once the new signals are installed ACHD will monitor how people react to the improvement. If the signals work well they may be installed at other locations around Ada County.

Intersections receiving new left-turn signal (click here for map):

• State/Plantation/Bloom

• State/Marketplace

• State/Willow

• State/Collister

• State/Ellens Ferry

• State/Pierce Park