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Fire engine red is an informal name, without particular chromatic specification, for an intense, bright red commonly used on emergency vehicles in the United States and Canada, mostly on, as the name implies, fire engines.
Most traditional older fire departments in larger U.S. central cities of major metropolitan areas use this color for their fire engines, but many suburbs and smaller cities now use the color lime or bright yellow for their fire engines because of its greater visibility at night. The initial research into fire appliance visibility was conducted by the City of Coventry (UK) Fire Brigade and Lanchester College of Technology in c. 1965. This research concluded that under the range of artificial street lighting in common use at the time yellow more generally retained its conspicuity under a variety of lighting color renderings. It was also more conspicuous in general road conditions in day time and during inclement weather. Research conducted by Dr Stephen Solomon, a New York optometrist, promoted the use of 'lime yellow' in the United States from the mid 1970s. Further research that endorsed the use of yellow for emergency vehicles generally was published in 1978 in Australia (Green, 1978, Emergency vehicle warning systems and identification, NSW Public Works Department).
Solomon conducted studies of the rate of vehicle accidents involving fire apparatus, concluding that the more conspicuously colored fire apparatus suffered a lower accident rate than the less conspicuously colored vehicles (red) used by the same fire department (Solomon, 1990, "Lime-yellow color as related to reduction of serious fire apparatus accidents -- the case for visibility in emergency vehicle accident avoidance" Journal of the American Optometric Association, 61(11) 827-830) and (Solomon and King, 1995 "Influence of Color on Fire Vehicle Accidents" Journal of Safety Research 26(1) 41-48).