The 2011 TMUTCD contains several changes that affect the design and operation of traffic signals. These changes include the addition of a Flashing Yellow Arrow (FYA) display for permissive left-turn operations. While a 5-section signal face with a circular green may still be used in a shared left-turn signal face, the use of a circular green indication in a separate left-turn signal face for permissive left turns has been prohibited. The flashing yellow arrow (or flashing red arrow) is now the only allowable indication for a permissive left/right-turn in a separate left/right-turn signal face.

Information provided in this section is for guidance and comes from of the TMUTCD.

Definitions of a Shared Left-Turn Signal Face and a Separate Left-Turn Signal Face as outlined in the TMUTCD are presented below.

Left-turning traffic is controlled by one of four modes as follows: protected only, protected permissive, permissive only, or variable by time of day.

Left-turn signal heads are required to have different arrangements as discussed below, depending on the signal face type (shared or separate) and the mode of operation (permissive only, protected only, protected permissive, variable, etc.). These requirements come from the 2011 TMUTCD and are listed below. To see these arrangements detailed graphically, see Table 5-1. It is an unofficial summary of Figures 4D-6 through 4D-12 of the 2011 TMUTCD.

An engineering study should be conducted to determine the appropriate left-turn signal control mode for signalized intersections. The study should consider left-turn volumes, crash history, 85th percentile (posted) speed, sight distance, number of left-turn lanes, number of opposing through lanes, pedestrian volumes, and opposing through volumes. Additionally, intersection geometry can affect the selection of the left-turn signal control mode. Intersections with wide medians, conflicting turning paths, non-standard alignments, etc., are also factors in determining left-turn signal mode.

There are many sources for determining left-turn control mode. Two flow charts obtained from recent research projects that may be used as an aid in determining the appropriate left-turn control mode are shown below.

Flashing Yellow Arrow (FYA) is an option for protected-permissive left-turn phasing. Careful consideration is needed in deciding where to install the FYA.

Some areas have existing FYA installations, while others have no experience with the display. Generally, implementation should consist of an initial pilot or demonstration project consisting of a few isolated intersections or a small section of corridor. The district should obtain local buy-in and approval, and provide press releases and information explaining where the FYA is being installed, what the FYA indications mean, how the motorists should interpret the indications, and why we are changing the existing set-up (the benefits).

Locations to consider for the pilot project installation of FYA protected-permissive left turns are typically sections of corridors with signalized intersections with the following characteristics:

Locations with the following characteristics are discouraged for use in the pilot project installation of FYA protected-permissive left turns:

It is better to be consistent in the application of left-turn treatment along a corridor for driver expectation. That said, it may not be practical to install FYA left turns consistently along a corridor. FYA left-turn operation requires a separate left-turn signal face. If a corridor is equipped with shared signal faces it may need new signal poles installed with longer mast-arms to cover the left-turn lane. Thus, it may be cost prohibitive to convert to FYA left-turn operation.

Installing FYA protected-permissive mode at a location that previously operated in protected-only mode should be considered only after careful study of the intersection. One research study of locations that were converted from protected-only mode to FYA protected-permissive mode saw an increase in the crash frequency. Do not remove protected-only left-turn phasing if opposing sight distance is inadequate for permissive left turns, operating speed is too great, roadway geometry is complicated, or there are too many opposing through lanes. If the protected-only left turn was installed for other safety reasons (crash prevention when under less restrictive phasing), care should be used in operating a possible FYA protected-permissive installation.

Installing protected-permissive FYA operation along emergency vehicle preemption routes requires special study and consideration. Work closely with emergency vehicles to provide the preemption operation that best fits their preference. Carefully consider whether to allow or terminate FYA for the opposing left during preemption. If the opposing FYA is to be turned off during preemption, the through phases will need to be terminated (go to all red) prior to dropping FYA for preemption.

For example, consider an intersection that is displaying Circular GREEN (for through) and FYA (left-turn lane) for both approaches of an arterial. Then, preemption activates to provide a protected through and left turn (Circular GREEN and GREEN ARROW dwell phase) to the approach for the emergency vehicle. From here, there are two possible states for the opposing left-turn FYA. It may continue to flash during the preemption dwell phase or it may be terminated. If it is decided to terminate the opposing left-turn FYA, then to go to all-red prior to displaying the dwell phase.

Variable mode operation is when signal operation changes between protected-only to protected-permissive mode, or between protected-permissive to permissive-only operation based on the time of day. It is possible with the 4-section FYA signal face when a study shows this type of operation to be beneficial. However, you must ensure that the controller is capable of switching between modes such that the flashing yellow arrow indication and the opposing through movement indication terminate together.

In other words, the controller should be capable of transitioning between modes without the flashing yellow arrow terminating while the opposing through movement stays green. Additionally, when switching between protected-permissive to permissive-only mode, ensure that the controller is capable of reassigning the left-turn detectors to call the associated through phases by time of day.

Installation of FYA left-turn operation should be coordinated with the District Public Information Office. Consider press releases with specific details on when the public can expect to see the new indications. Press releases should be prepared and sent out approximately two weeks or more in advance of conversion. Special attention should be given to the first installation in an area. If available, place portable changeable message signs in advance of the affected signals at least five days before the FYA activation date.

The majority of current TxDOT traffic signal equipment is compatible with FYA operation. TxDOT signal cabinets, as currently equipped, can be modified to perform FYA. Prior to installing or converting an intersection to FYA left-turn operations, it will be necessary to ensure that there is adequate field wiring, the signal controller cabinet has adequate channels (load switches), and the controller and Malfunction Management Unit (MMU) are capable of FYA operation. Configuration of the traffic signal cabinet may be dependent on several conditions at the intersection such as the controller requirements, the monitor requirements, the cabinet size and available load switches, and whether pedestrian signals are being utilized. Careful planning is required to ensure a successful installation.

Controller manufacturers have standardized FYA operation, however, there may be older equipment that is not FYA compatible. Cabinet modification will depend on controller make and model. An MMU capable of FYA operation is required. If needed, install a new MMU recommended by the controller manufacturer. A modification to the cabinet flash programming is required. Contact the manufacturer representative or the TRF-TM Engineering Support Branch for assistance if needed.

While the 2011

TMUTCD

does not require this signing, a "Left-Turn Signal - Yield on Flashing Arrow" (R10-17T) sign should be installed adjacent to the new head for clarification. If the FYA face is to be installed at an existing location with a 5-section face, verify the sign can be installed and ensure any conflicting signs, such as the "Left Turn Yield on Green” sign (R10-12), is removed if in place.

Signal observations should be performed periodically as discretely as possible, and particularly during the times where the phasing has changed from the previous installation. When converting left-turn signal operations to FYA protected-permissive, be sure to observe driver behavior, especially in cases where the intersection previously operated in a protected-only mode.

With the initial FYA installations in your area, monitor the crash data for at least one year after installation.

The 2011

TMUTCD

provides Figure 4D-3, "Recommended Vehicular Signal Faces for Approaches with Posted, Statutory, or 85th Percentile Speed of 45 mph or Higher," and Table 4D-1, “Recommended Minimum Number of Primary Signal Faces for Through Traffic on Approaches with Posted, Statutory, or 85th-Percentile Speed of 45 mph or Higher” (Shown in Figures 5-2 and 5-3 below). Requirements from the table are a "should condition," The table should be consulted for minimum number and location of primary signal faces for through traffic.