The City of West Des Moines has installed a new traffic signal display at 110 intersections to provide a safer, more efficient left turn for motorists.  The flashing yellow arrow display replaces the circular green ball indication for left turns at signalized intersections.  The City has received funding from the Iowa Department of Transportation’s Traffic Safety Improvement Program to install the flashing yellow arrow left turn signal heads at the remaining 70 intersections that use the green arrow and green ball combination for the protected-permitted left turn signals.  The new display will also be implemented when new signals are installed.

How does it work?

A steady red arrow means that drivers wishing to turn left must stop and wait at the stop line.

A steady yellow arrow means drivers should not enter the intersection if they can stop safely.

A flashing yellow arrow means left turns are permitted, but you must first yield to oncoming traffic and pedestrians, and then proceed with caution.

The steady green arrow still means that the drivers making the left turn have the right-of-way to make the protected left turn and the oncoming traffic has a red light. 

The flashing yellow arrow replaces the green ball indication for a yielding left turn, but it does not replace the steady yellow arrow.

Why the change?

This change us the result of a new national standard for permissive left-turn operation, as adopted by the Federal Highway Administration (FHWA).  National studies conducted for the FWHA demonstrated that drivers made fewer mistakes with the new signals than with the traditional circular green ball indication.  Many drivers perceived the circular green ball to mean “go” and forgot to yield to oncoming traffic when turning.

Why is it a better left-turn signal?

• It’s safer.  According to preliminary evaluations, FWHA estimates that the new display results in a 30% reduction in left-turn collisions.  This is the 2^nd highest type of crashes in West Des Moines behind rear-end collisions.

• It’s more efficient.  The new display gives traffic engineers more options to handle variable traffic volumes during different times of the day.

• It’s more consistent.  As the new signals are introduced throughout the United States, you’ll see the same left-turn signals in every state.

Does it really reduce left-turn crashes?

Left turn crash data for thirteen intersections in West Des Moines was examined where the flashing yellow arrow left turn signal had been installed for at least one year.  The average annual number of left turn crashes for the previous four years was determined for the thirteen intersections as well as the number of left turn crashes in the year since the flashing yellow left turn signals had been installed.  The data indicated the following:

• Prior to flashing yellow arrow signal = 20 crashes/year
• One year after flashing yellow arrow signal = 10 crashes/year

In West Des Moines we are experiencing a reduction in left turn crashes at intersections with the flashing yellow arrow left turn signal.  The flashing yellow arrow left turn signal is providing a safer, more efficient, and more consistent left turn signal display to the motorists that drive the streets of West Des Moines.