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The Indiana Department of Transportation will begin using flashing yellow arrow traffic signal indications for protected/permissive left turns as part of signal modernizations on the state highway system. A protected/permissive left-turn signal is a signal face that contains a protected phase where left turners have the exclusive right-of-way and a permissive phase where left turners may make their turn if there are no opposing through vehicles.
Over the next several years, INDOT will be installing new four-section signal heads – which include a flashing yellow arrow. These signals will replace the left-turn traffic signals that do not include a flashing yellow arrow. At certain locations with vertical clearance limitations, INDOT may use an alternative three-section signals to display flashing yellow arrow indications.
The new left-turn signal will improve intersection efficiency by allowing more left turns by enabling drivers to utilize cross-traffic gaps. The new signals also will improve intersection safety by providing an instruction to left-hand turning drivers that remains for the entire signal phase.
A flashing yellow arrow for left turns at an intersection means that motorists should slow down and use caution when turning, and must yield the right-of-way to oncoming traffic as well as any pedestrians who may be crossing the intersection.
A flashing yellow arrow signal offers operational benefits that are not possible with the current five-section (also known as “doghouse”) left turn signals. A signal’s left turn phase could operate as protected only with the green and solid yellow arrows during certain hours of the day and then as protected/permissive during other hours of the day, depending upon typical traffic flows.
The flashing yellow arrow may also be displayed before and/or after the protected green and solid yellow left turn arrows to improve traffic flow. The steady yellow arrow retains its standard meaning: The left-turn signal is about to change to a steady red arrow and drivers should prepare to stop or, if they have already entered the intersection, they should complete the left turn when oncoming traffic has cleared.
The Federal Highway Administration has adopted the flashing yellow arrow as a preferred practice for protected/permissive left-turn operations. The first new signal in Indiana will be installed in late September/early October 2013 at U.S. 40 and Salisbury Road in Richmond, Ind. The cost per intersection for this upgrade is approximately $900.
A National Cooperative Highway Research Program study demonstrated that drivers found flashing yellow left-turn arrows more understandable than traditional yield-on-green indications. The flashing yellow arrow will communicate to drivers that they must proceed with care and decide if there is a sufficient gap in oncoming traffic to make a left turn.
The flashing yellow left-turn arrow has been shown to be especially effective at intersections with high volumes of traffic and also provides traffic engineers with more options to handle variable traffic volumes. Motorists have more opportunities to make a left turn with a flashing yellow left-turn arrow than with traditional protected/permissive left-turn signals.
Traffic Engineering Director
Indiana Department of Transportation
100 N. Senate Ave., IGCN 955
Indianapolis, IN 46204