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Interpretation Letter 6(09)-36 (I) — Warning Lights on 36-inch Cones

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U.S. Department of Transportation
Federal Highway Administration

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

October 1, 2015

In Reply Refer To: HOTO-1

Mr. Jerry Britton
Unipart Dorman
173 Main Street
Bath, Ontario K0H 1G0

Dear Mr. Britton:

Thank you for your recent letter requesting an Official Interpretation of Sections 6F.64 and 6F.83 of the 2009 Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD).

Your company has developed a sequential warning light system that is intended to provide additional directional information to road users approaching a lane closure where 36-inch cones are utilized for channelization. The proposed method of attaching each warning light to the cone involves sliding the lens and case onto the top of the cone. The light slides downward until it tightens on the conical shape of the cone. With the proposed mounting method of the warning light, the housing would obscure approximately 2.75 inches of the upper retroreflective stripe that is required by Section 6F.64 of the MUTCD.

The warning lights utilized in your system have prismatic retroreflective surfaces on the perimeter of the lens in addition to a light source. This retroreflective band around the lens is intended to offset the fact that the retroreflective stripe is partially obscured.

Section 6F.83 of the MUTCD specifically allows the use of warning lights on channelizing devices.

If cones are to be used at night, Section 6F.64 requires a 6-inch retroreflective stripe located 3 to 4 inches from the top of the device and a second 4-inch retroreflective stripe located approximately 2 inches below the upper stripe. The intent of these stripes is to provide nighttime visibility to road users.

Because the MUTCD allows for the use of warning lights on channelizing devices and because the warning light itself has retroreflective properties on the portion that partially obscures the retroreflective stripe, it is the Federal Highway Administration's (FHWA) official interpretation that the use of the sequential warning light system as described meets the intent of Section 6F.64 of the MUTCD in providing retroreflectivity to the cone for nighttime visibility. Because the MUTCD provides a range of mounting heights for the required retroreflective stripes on the cones, it is recommended that the stripes be applied at the lower heights specified when lights are intended to be mounted to the cones so that as little of the upper retroreflective stripe is obscured as possible.

Please be aware that the requirements of the MUTCD regarding crashworthiness of traffic control devices apply to your device when used in the specific combination described. This official ruling does not constitute, with respect to crashworthiness, acceptability of your device on roads open to public travel or eligibility for Federal-aid reimbursement. Please refer to the FHWA Office of Safety's Web site at for additional information on crashworthiness of roadside hardware and work zone devices.

For recordkeeping purposes, we have assigned your request the following official ruling number and title: "6(09)-36 (I) — Warning Lights on 36-inch Cones." Please refer to this number in any future correspondence regarding this topic.

Please contact Mr. Ken Wood at if you have any further questions concerning this matter.

Sincerely yours,

Original signed by:

Mark R. Kehrli
Director, Office of Transportation Operations