**NCHRP Report 493,** the report produced at the conclusion of the NCHRP
3-54 project on protected/permissive left turn signals, specified on
Page 91 that there could be some variations on the exclusive signal
arrangement of the protected/permissive flashing yellow arrow display.
These variations are as follows:

-   *The agency may use a circular red indication in lieu of the red
    arrow.*

-   *A three-section all-arrow display using the center section as a
    change interval and the permissive interval is allowed, provided
    that all yellow change intervals for the approach are initiated
    simultaneously.*

-   *A ﬁve-section display may be used.*

Even though the main display for the flashing yellow arrow should be the
four-section signal face (or the three-section signal face with the
dual-arrow signal section as described in NCHRP Report 493), I suggest
that some of these variations as suggested by NCHRP Report 493 could be
incorporated into the MUTCD in some situations. Below are my personal
opinions about them as far as the MUTCD is concerned:

**CIRCULAR RED in use instead of the Red Arrow**

Since the RED ARROW is being phased in for protected-only mode left
turns as a requirement, and since the CIRCULAR RED is being phased out
for protected-only mode left turns with a 15-year compliance period, the
CIRCULAR RED should also not be allowed with the flashing yellow arrow
protected/permissive left turn display. The only exceptions to this rule
should be for protected/permissive left turns onto one-way streets when
is intended to allow left turns on red, or for a signal display that is
in accordance with Section 4D.25.

**Three-Section Flashing Yellow Arrow Displays**

The Interim Approval and the proposed Standard in the MUTCD already
allow the following three-section configurations that use a dual-arrow
signal section, that display the flashing yellow arrow and steady green
arrow from the same signal section, where signal head height limitations
won't permit the use of a four-section signal display. The allowed
configurations are as follows:

  -------------------- ------------------- ------------------------------
  **Steady left-turn   **Steady left-turn  **Dual-mode steady GREEN ARROW
  RED ARROW**          YELLOW ARROW**      and flashing YELLOW ARROW**

  -------------------- ------------------- ------------------------------

  -----------------------------------------------------------------------
  **Steady left-turn RED ARROW**

  **Steady left-turn YELLOW ARROW**

  **Dual-mode steady GREEN ARROW and flashing YELLOW ARROW**
  -----------------------------------------------------------------------

A different arrangement of a three-section signal face uses the same
signal section to display both the flashing YELLOW ARROW and steady
YELLOW ARROW signal indications, which does not conform to the current
Interim Approval. It is my understanding that Jackson County, Oregon is
experimenting with this display. However, I have a different opinion
from NCHRP Report 493: That the flashing YELLOW ARROW and steady YELLOW
ARROW signal indications may be permitted to be displayed from the same
signal section ONLY if the flashing yellow arrow is ALWAYS followed by a
GREEN ARROW.

So these display configurations could be:

  ---------------------- ----------------------------- -------------------
  **Steady left-turn RED **Steady and/or flashing      **Left-turn GREEN
  ARROW**                left-turn YELLOW ARROW**      ARROW**

  ---------------------- ----------------------------- -------------------

  -----------------------------------------------------------------------
  **Steady left-turn RED ARROW**

  **Steady and/or flashing left-turn YELLOW ARROW**

  **Left-turn GREEN ARROW**
  -----------------------------------------------------------------------

The ONLY acceptable sequence with this display would be: flashing YELLOW
ARROW, then GREEN ARROW, then steady YELLOW ARROW, then steady RED
ARROW. Transition from flashing YELLOW ARROW directly to steady YELLOW
ARROW would not be permitted with this signal face, thus limiting the
display's usefulness.

This display could be used, for example, at a high-volume left turn from
a major street, a two-phase signal that only regulates the left turn and
the opposing through movement where the adjacent through movement is
either independently controlled or unsignalized (i.e. no cross traffic
that requires the left-turn movement to completely stop). An example
would be a protected/permissive left turn onto a freeway ramp where the
adjacent through movement has a continuously-illuminated single-section
straight-through GREEN ARROW indication. I don't see the point of
requiring the flashing yellow arrow and the steady yellow arrow to be
displayed from different signal sections in these unusual cases where
the flashing yellow arrow is always followed by a green arrow.

Note that this display could also be operated in protected-only mode,
where the flashing yellow arrow is omitted.

**Five-Section Flashing Yellow Arrow Displays**

This could be useful in retrofitting an existing "Dallas Display" PPLT
signal, and may be easier to wire in some controllers. The overlap on
the existing Dallas Display is an overlap between the opposing through
movement and the left turn, where the circular green indication is
displayed during both the permissive left turn and the protected left
turn movements. (The protected left turn movement always displays both
the green ball and the green arrow simultaneously.) The only software
changes would be:

-   Flash the green output on the overlap. (The green ball would be
    replaced with a yellow arrow.)

-   Implement special logic that will omit the overlap whenever the
    green arrow and steady yellow phase outputs are illuminated.

The 5-section flashing yellow arrow signal face would incorporate two
steady yellow arrow signal sections. One steady yellow arrow would be an
overlap output, and the other steady yellow arrow would be a phase
output. This is almost identical to the Dallas Display in a 5-section
head, but the signal indications may have to be rearranged.

There would be three acceptable signal configurations:

Horizontally-arranged signal head:

+-----------+---------------+--------------+---------------+----------+
| *         | **Steady      | **Steady     | **Flashing    | **L      |
| *Steady** | left-turn     | left-turn    | left-turn     | eft-turn |
|           | YELLOW ARROW  | YELLOW ARROW | YELLOW        | GREEN    |
| **        | (displayed    | (displayed   | ARROW**       | ARROW**  |
| left-turn | only after    | only after   |               |          |
| RED       | the flashing  | the steady   | **(overlap    | **(phase |
| ARROW**   | yellow        | green        | output)**     | o        |
|           | ar            | a            |               | utput)** |
|           | row---overlap | rrow---phase |               |          |
|           | output)**     | output)**    |               |          |
+-----------+---------------+--------------+---------------+----------+

Vertically-arranged signal head, inline:

+-----------------------------------------------------------------------+
| **Steady left-turn RED ARROW**                                        |
+-----------------------------------------------------------------------+
| **Steady left-turn YELLOW ARROW**                                     |
|                                                                       |
| **(displayed only after the flashing yellow arrow---overlap output)** |
+-----------------------------------------------------------------------+
| **Steady left-turn YELLOW ARROW**                                     |
|                                                                       |
| **(displayed only after the steady green arrow---phase output)**      |
+-----------------------------------------------------------------------+
| **Flashing left-turn YELLOW ARROW (overlap output)**                  |
+-----------------------------------------------------------------------+
| **Left-turn GREEN ARROW (phase output)**                              |
+-----------------------------------------------------------------------+

Vertically-arranged signal head, "doghouse" arrangement: (And it is my
understanding that the State of Idaho is experimenting with this display
in some locations.)

+-----------------------------------+-----------------------------------+
| **Steady left-turn RED ARROW**    |                                   |
+-----------------------------------+-----------------------------------+
| **Steady left-turn YELLOW ARROW** | **Steady left-turn YELLOW ARROW** |
|                                   |                                   |
| **(displayed only after the       | **(displayed only after the       |
| steady green arrow---phase        | flashing yellow arrow---overlap   |
| output)**                         | output)**                         |
+-----------------------------------+-----------------------------------+
| **Left-turn GREEN ARROW**         | **Flashing left-turn YELLOW       |
|                                   | ARROW**                           |
| **(phase output)**                |                                   |
|                                   | **(overlap output)**              |
+-----------------------------------+-----------------------------------+

Note that, during the transition from flashing yellow arrow to steady
green arrow, neither steady yellow arrow would be displayed. The signal
would go directly from the flashing yellow arrow to the steady green
arrow. So, in effect, these five-section signal heads would provide the
same signal sequences as the flashing yellow arrow displays that are
currently covered under Interim Approval IA-10.

This complies with other provisions of the current Interim Approval and
the proposed MUTCD standard that requires flashing yellow arrow and
steady yellow arrow to be displayed from different signal sections (that
is, a moving arrow from the permissive left turn to the yellow change
interval).

Again, this 5-section display should ONLY be used where controller,
cabinet, and/or other hardware limitations will not permit the use of
the 3-section or 4-section display with one steady YELLOW ARROW signal
section and where the phase outputs require the display of the steady
YELLOW ARROW from different signal sections in the same sequence (for
example, as a retrofit of a Dallas Display).

**Another variation of the 4-section Flashing Yellow Arrow Display**

This is a variation of the "doghouse" 5-section flashing yellow arrow
display except that it only has 4 sections. This display could
potentially be used where signal head height limitations won't permit
the use of an inline four-section vertical display AND where the agency
has not approved the use of a dual-arrow signal section.

This display would be as follows:

  ----------------------------------- -----------------------------------
  **Steady left-turn RED ARROW**      

  **Steady left-turn YELLOW ARROW**   

  **Left-turn GREEN ARROW**           **Flashing left-turn YELLOW ARROW**
  ----------------------------------- -----------------------------------

**Other thoughts:**

The flashing yellow arrow PPLT signal should be required to be used for
PPLT if the adjacent through movement is unsignalized. The flashing
yellow arrow PPLT should also be required if it is needed to eliminate
the "yellow trap" condition or if protected only phasing is needed by
time of day.

Dallas Displays should be phased out with a compliance period, being
replaced with a flashing yellow arrow. I suggest 15 years (same as for
red arrows being required for protected-only left turns). This is to
completely eliminate the display of conflicting signal indications in
different signal faces (one or more signals displaying CIRCULAR RED with
one or more signals displaying CIRCULAR GREEN) on an intersection
approach.

The use of shared signal faces should be allowed to continue, except
when a yellow trap condition exists in which an "ONCOMING TRAFFIC
HAS/MAY HAVE EXTENDED GREEN" sign was required under the 2003 MUTCD.
Yellow traps in a shared signal face with the "ONCONING TRAFFIC HAS/MAY
HAVE EXTENDED GREEN" signs should have a flashing yellow arrow signal
display installed with a compliance period of sooner than that for the
retrofit of Dallas Displays as described above.