U.S Department of Transportation
Federal Highway Administration
400 Seventh St., SW.
Washington, D.C. 20590

September 10, 2001
Refer to: HOTO-1

Mr. Michael Robertson
Rail Safety and Carriers Division
California Public Utilities Commission
505 Van Ness Avenue
San Francisco, CA 94102-3298

Dear Mr. Robertson:

We received a copy of your July 20 letter to Mr. William Watson, Chair of the Rail Technical Committee of the National Committee on Uniform Traffic Control Devices. Since the Federal Highway Administration has the responsibility for the Manual on Uniform Traffic Control Devices (MUTCD), we will provide the interpretation you requested. Specifically, you requested an interpretation on the size of background that is required for the 8 in and 12 in signals.

Section 8D.02, "Flashing-Light Signals, Post Mounted," requires that the "flashing-light units shall use either 200 mm (8 in) or 300 mm (12 in) nominal diameter lenses." The section also provides guidance that the principles in Chapter 4D be considered when deciding which size lens to use for highway-rail grade crossings. Since your issue is the size of the background for the flashing-light signals, Part 8 is the area of the MUTCD to be followed.

Section 8D.02 refers to Figure 8D-1, "Composite Drawing of Active Traffic Control Devices for Highway-Rail Grade Crossings Showing Clearances." In this figure, the background is shown as having either a 250 mm (10 in) radius or a 300 mm (12 in) radius. It was the Federal Highway Administration's intent for the 250 mm (10 in) radius background to be used with the 200 mm (8 in) diameter flashing-light signal and the 300 mm (12 in) radius background to be used with the 300 mm (12 in) diameter flashing-light signal. Since there is no current guidance on which size background to use with which size flashing-light signal, we interpret your crossing to be in compliance with the MUTCD. We will clarify this in a future rulemaking action in the Federal Register.

We have assigned this interpretation the number and name 4-231-I, "Size of Background for Flashing-Light Signals." Please refer to this number in any future correspondence on the subject.

Thank you for requesting clarification on this issue.

Sincerely yours,

Shelley J. Row, P.E.
Director, Office of Transportation Operations