The University of Tennessee, Knoxville


TTAP Newsletter: RoadTalk

MUTCD Notes - Just a Reminder!

by Dr. Airton Kohls

The 2009 MUTCD has incorporated some new Standards and new Guidance regarding the positioning of Traffic Signal faces. I have noticed lately that some locations are not following some of these recommendations and rules, (even on new or reconstructed installations), leaving the door open for potential liability issues! First, let me address the positioning and arrangement of shared signal faces for protected/permissive left turn movements:

- Section 4D-13 provides GUIDANCE stating that signal faces containing a circular green signal indication for a permissive left-turn should not be located overhead above an exclusive left-turn lane or the extension of the lane, nor should they be post-mounted on the far side median in front of the left-turn lane. This recommendation applies only to new or reconstructed signal installations. It doesn’t happen very often that a driver will incorrectly interpret the circular green over the left-turn lane as meaning they have the right-of-way to "go" without yielding. But when it does happen, the resulting crash can be serious or fatal!

Here is the typical position and arrangement of shared signal faces for protected/permissive mode left turns, as described on Section 4D-20 (Figure 4D-11) of the MUTCD:


Notice that placing the shared signal display over the lane line or to the right of it helps to promote the idea that the signal display with the circular green is being shared by the left turn lane and the thru lane, and reduces the chance that a left turning driver will misinterpret the circular green as a "go, you have the right of way" message.

Now, Section 4D-19 addresses the issue that protected only mode left-turn faces must use a red arrow, not circular red. This enhances uniformity by requiring States and local agencies to use a red arrow instead of a circular red for protected-only mode turn signals. Red arrow signal indications have been in use for over 35 years, are extensively implemented for protected turn movements in the majority of the States, are well understood by road users, present a clear message regarding which movement is prohibited when the red indication is displayed, and eliminate the need for a supplemental LEFT TURN SIGNAL sign. Here is the MUTCD Standard Section 4D-19: "If a separate left-turn signal face is provided for a protected only mode left turn, it shall meet the following requirements (see Figure 4D-10):


- It shall be capable of displaying the following signal indications: steady left-turn RED ARROW, steady left-turn YELLOW ARROW, and left-turn GREEN ARROW. Only one of the three indications shall be displayed at any given time. A signal instruction sign shall not be required with this set of signal indications. If used, it shall be a LEFT ON GREEN ARROW ONLY (R10-5) sign."

Shared signal face for protected/permissive mode left turn inconsistent with 2009 MUTCD Section 4D-13 and Figure 4D-11 guidance.
Existing separate protected-only left-turn phase signal faces that include a CIRCULAR RED signal indication instead of a left-turn RED ARROW signal indication may be retained for the remainder of their useful service life. By "existing" FHWA instructed to be those signal faces permitted until the 2009 MUTCD became effective.