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Interpretation Letter 2(09)-79 (I) - Radar Speed Feedback Signs

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U.S. Department of Transportation
Federal Highway Administration

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

October 22, 2013

In Reply Refer To: HOTO-1

Amy Gamble, PE
Traffic Operations Engineer
Vermont Agency of Transportation
1 National Life Drive
Montpelier, VT 05633-5001

Dear Ms. Gamble:

Thank you for your e-mail requesting an official interpretation regarding the use of strobes and flashing displays with radar speed feedback signs. The 2009 edition of the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD), allows the use of a "changeable message sign that displays to approaching drivers the speed at which they are traveling to be used in conjunction with a Speed Limit sign." These signs include the commonly referred to radar speed feedback signs.

Since radar speed feedback signs are changeable message signs, provisions for their use and application are contained in Chapter 2L of the MUTCD. Specifically, Paragraph 1 in Section 2L.04 provides that changeable message signs shall not include advertising, animation, rapid flashing, dissolving, exploding, scrolling, or other dynamic elements.

With respect to using strobe effects, Paragraph 4 of Section 2A.15 specifically provides that strobe lights shall not be used to enhance the conspicuity of highway signs.

For these reasons, it is the FHWA's interpretation that the MUTCD specifically prohibits the use of flashing displays and strobe light technology on changeable message signs to include radar speed feedback signs. For recordkeeping purposes, we have assigned this Official Interpretation the following number and title, "2(09)-79 (I) - Radar Speed Feedback Signs." Please use this number and title in any future correspondence. If you have further questions on this matter, please contact Mr. Eric Ferron of our MUTCD Team at 720-963-3206 or

Sincerely yours,

Original signed by:

Mark R. Kehrli
Director, Office of Transportation Operations