United States Department of Transportation. Federal Highway Administration. (December 2007). "Manual on Uniform Traffic Control Devices"(PDF). Federal Highway Administration. pp. 6F–33. Retrieved 2009-10-24.
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Official Florida Driver's Handbook 2008 (1 October 2008), Division of Driver's Licenses, Florida Department of Highway Safety and Motor Vehicles! Web-based PDF. Chapter 4, Section 7 "Special Signs." Channeling Devices.
