Why was the previous MUTCD guidance that recommended yellow signal head housings eliminated?

The 1988 and prior editions of the MUTCD stated that "it is desirable that signal head housings be yellow." This language was not a strong recommendation and, as such, it was not a uniform practice by many agencies. In the 2000 MUTCD, with reformatting of all text into standards, guidance, options, and support, this became a Guidance statement: "To obtain the best possible contrast with the visual background, signal housings should be highway yellow."

This guidance was deleted effective with the 2003 edition, because there is no consensus that yellow signal housings universally provide the best contrast in all of the various environments. In actual practice, it is estimated that far fewer than 50 percent of the signal heads in the United States are highway yellow. California, New York State, and many other jurisdictions with very large numbers of signals require their signal heads to be other colors, such as green, black, gray, brown, etc. Regardless of the color of the signal ... more.

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