[3] Traditional fire departments in large U.S. central cities and major metropolitan areas use this color on fire engines, but many suburbs and smaller cities use the color lime or bright yellow for their fire engines because of its greater visibility at night.

It concluded that under the range of artificial street lighting in common use at the time, yellow better retained its conspicuity than red.

Yellow was also more conspicuous in general road conditions in the daytime and during inclement weather.

Research conducted by Stephen Solomon, a New York optometrist, promoted the use of "lime yellow" in the United States from the mid-1970s.

[5][6] Further research supporting the use of yellow for all emergency vehicles was published in 1978 in Australia.