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

Refer to: HOTO-1

September 27, 2001

Mr. Michael K. Curtit
Technical Support Engineer
Missouri Department of Transportation
105 West Capital Avenue
Jefferson City, MO 65102

Dear Mr. Curtit:

Your recent series of e-mail exchanges with Ms. Mary Ridgeway of the Federal Highway Administration’s (FHWA) Missouri Division Office was forwarded to this office for reply. In your e-mails you requested an interpretation of Section 4D.06, Standard, item A, of the Manual on Uniform Traffic Control Devices (MUTCD) in regard to whether a "Dallas left turn" type of signal display provided to a Permissive Only Mode left turn is in conformance with the MUTCD.

The intent of the FHWA was to include text in Section 4D.06 to specifically allow the use of what is commonly referred to as "Dallas phasing displays" in the Protected/Permissive Mode. Experimentations and evaluations of the Dallas phasing that led to the decision to include this in the 2000 MUTCD all involved only protected/permissive mode left turns. Therefore, item A in the Standard of Section 4D.06 does not contemplate the application of a display such as you have used in Missouri for Permissive Only Mode left turns. The intent of item A is to require any separate or shared signal faces that control a Permissive Only Mode left turn movement to display the same color circular indication as the adjacent through signal face or faces, regardless of whether the face is shielded, hooded, louvered, etc.

We do recognize that the Missouri application is in the spirit of what the Dallas phasing display is intended to accomplish in terms of eliminating the "yellow trap" for the left turn movement. The FHWA will consider making revisions to Section 4D.06 to specifically address your application in the next revision of the MUTCD.

Thank you for your request. If you have any questions, please call Mr. Scott Wainwright at 202-366-0857. Please note that we have assigned your request the following official interpretation number and title: "4-234 (I)—Permissive Only Mode Dallas Displays." Please refer to this number in future correspondence.

Sincerely yours,

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

FHWA: HOTO?1:SWainwright:ds:60857:9-27-01
cc: HOTO?1 HOST?1 HOTO-1(Huckaby/Schoene/Wainwright)
All Resources Centers, HOP-MO(2) Mr. Bob Garrett, NCUTCD
Mr. Roger Wentz, ATSSA Chron 3408 Reader 3408