‘Walking person’ confusion

I have recently noticed that the pedestrian signals at some intersections in Washington, DC show a flashing walking person during the ‘walk’ signal phase, where the walking person would not ordinarily flash. Because these are countdown signals, there’s no ambiguity as to the time remaining to cross, but there’s still the risk that the nonstandard signal indication could confuse pedestrians.

The Manual on Uniform Traffic Control Devices, published by the Federal Highway Administration, regulates traffic control devices like these pedestrian signals. States can either adopt the national MUTCD unchanged, adopt the national MUTCD with a state-specific supplement, or adopt a state MUTCD “that is in substantial conformance with” the national MUTCD. FHWA indicates that DC has adopted the 2003 MUTCD with no state supplement.

Here is the relevant text from the 2003 MUTCD:

A flashing WALKING PERSON (symbolizing WALK) signal indication has no meaning and shall not be used.

The matter would thus appear to be clear-cut: pedestrian signals should never display a flashing walking person. However, there are various methods by which traffic control devices other than those specified in the adopted edition of the MUTCD may be used. The FHWA issues interpretations, approves experimental traffic control devices, responds to requests for changes, and issues interim approvals for new traffic control devices not covered in the adopted MUTCD. I have searched all four of these listings and found nothing pertaining to the use of a flashing walking person. Therefore, the text of the 2003 MUTCD governs.

In addition, DDOT publishes a Design and Engineering Manual, which states:

Pedestrian signal faces shall be operated so as to display four indications: Steady WALKING PERSON, flashing upraised HAND, and steady upraised HAND, and a numerical count-down display. All signalized crosswalk in Washington D.C. are equipped with countdown LED modules. All two section pedestrian signal heads in the city shall feature the Raised Hand / Walking Person combination module in the top section and the countdown LED module in the bottom section.

This leaves one final question: if the flashing walking person is not to be used, why would a signal controller even be capable of generating that indication? The answer comes from the book Human Factors in Traffic Safety:

The flashing WALK signal was used to warn of vehicles turning, but is no longer in use in the U.S.

I can only assume that signal controllers are still capable of being configured to display a flashing walk indication when conflicting traffic may be present, and this would imply that the signal controllers at those intersections exhibiting the flashing walk indication have become misconfigured (whether intentionally or otherwise).

(Finally, a brief note for disambiguation purposes: what traffic engineers call a ‘signal indication’ is the same thing that would be called a ‘signal aspect’ in rail terminology.)