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Interpretation Letter 2-638 (I) - Color of Light Emitting Diodes (LEDs)

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U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Avenue, SE.
Washington, D.C. 20590

January 31, 2008

In Reply Refer To: HOTO-1

Mr. Ernest D. L. Huckaby
MUTCD Consultant Services
13402 Caribou Court
Fort Washington, MD 20744

Dear Mr. Huckaby:

Thank you for your letter of January 6 requesting an interpretation regarding the use of light emitting diodes (LEDs) in regulatory and warning signs and requesting a change to add additional language to the Manual on Uniform Traffic Control Devices (MUTCD) to clarify the current language for the application of LEDs.

Your request to change the MUTCD is of interest to the Federal Highway Administration (FHWA) and will be added to the docket comments for the Notice of Proposed Amendments (Docket No. FHWA-2007-28977). Please note that the following change was proposed to Section 2A.07 for the application of LEDs:


A module of multiple LED units used as a closely-spaced, single light source shall only be used within the sign face for if contained within the legends or within the symbols.
Except for the STOP/SLOW paddles (see Section 6E.03) used by flaggers and the STOP paddles (see Section 7D.05) used by adult crossing guards, neither individual LED pixels nor groups of LEDs shall be used within the background area of a sign.

In response to your request for an interpretation of Section 2A.08 to clarify the color of LEDs the following is provided:

  1. The color of LEDs applied to a standard warning sign shall all be yellow to match the yellow background of a standard warning sign and white LEDs cannot be used.
  2. The color of LEDs applied to a standard regulatory sign with a black border shall all be white.
  3. The color of LEDs applied to a red background standard regulatory sign, such as STOP, YIELD, DO NOT ENTER or WRONG WAY signs shall all be red or white.

I hope this information satisfactorily addresses your inquiry. We have assigned the following official ruling number to your request: "2-638 (I) - Color of Light Emitting Diodes (LEDs)." Please refer to this number in any future correspondence. If we can be of further assistance on this matter, please contact Mr. Fred Ranck at 708-283-3545.

Sincerely yours,

/s/ Robert Arnold

Robert Arnold
Director, Office of Transportation Operations