Interpretation Letter 4(09)-11 (I) - Flashing Beacons Maximum Mounting Height

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U.S. Department of Transportation
Federal Highway Administration

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

June 29, 2011

In Reply Refer To: HOTO-1

Mr. Bob Pappe
State Traffic/Roadway Engineer
Oregon Department of Transportation
1158 Chemeketa Street NE
Salem, Oregon 97301

Dear Mr. Pappe:

During the course of development of the Oregon Supplement to the 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD), your staff questioned a provision in Section 4L.03 that specifies a maximum mounting height of 19 feet above the pavement for flashing warning beacons mounted over the roadway. We are writing to provide an Official Interpretation of that provision.

It is our Official Interpretation that the maximum mounting height of a flashing warning beacon mounted over the roadway shall be 25.6 feet, measured from pavement surface to the top of the housing of the beacon. Our reasoning for this interpretation is as follows.

The pertinent text of the 2009 MUTCD is as follows:

Section 4L.01 (General Design and Operation of Flashing Beacons), paragraph 02: "Flashing Beacon units and their mountings shall comply with the provisions of Chapter 4D, except as otherwise provided in this Chapter."
Section 4D.15 (Mounting Height of Signal Faces), paragraph 01: "The top of the signal housing of a vehicular signal face located over any portion of a highway that can be used by motor vehicles shall not be more than 25.6 feet above the pavement."
Section 4L.03 (Warning Beacon), paragraph 05: "If a Warning Beacon is suspended over the roadway, the clearance above the pavement shall be a minimum of 15 feet and a maximum of 19 feet."

In the 1988 and earlier editions of the MUTCD, the maximum mounting height of vehicular signal faces and of warning beacons was specified to be 19 feet above the pavement, measured to the bottom of the housing. In the final rule adopting the 2000 edition of the MUTCD, Section 4D.15 was revised to specify a maximum mounting height of vehicular signal faces of 25.6 feet above the pavement, measured to the top of the signal face housing. This change was intended to assure adequate visibility of the signal indication at the top of a 5-section vertically-arranged signal face. At that time, the provisions relating to the maximum mounting height of flashing warning beacons mounted over the roadway should have also been changed to 25.6 feet, to be consistent with the revision in Section 4D.15, since there is no reason why flashing warning beacons must be mounted at a lower height above the road than the top of a vehicular signal face. However, due to an inadvertent oversight, that change regarding flashing warning beacons was not made at the time of the 2000 edition, nor was it noticed or proposed for change in the 2003 or 2009 editions.

Accordingly, it is our Official Interpretation that the maximum mounting height of a flashing warning beacon mounted over the roadway shall be 25.6 feet, measured from pavement surface to the top of the housing of the beacon. Paragraph 05 of Section 4L.03 should be deleted. The general provision in paragraph 02 of Section 4L.01 adequately governs the minimum and maximum mounting heights of flashing warning beacons, as it does for other types of beacons. For the next edition of the MUTCD, we will consider proposing revisions to the Section 4L.03 to formally correct this inadvertent error.

Thank you for bringing this matter to our attention. Please note that we have assigned your request the following official interpretation number and title: "4(09)-11 (I) – Flashing beacons Maximum Mounting Height." Please refer to this number in any future correspondence regarding this issue.

Sincerely yours,

Original signed by:

Mark R. Kehrli
Director, Office of Transportation Operations