Since providing interim approval for the optional use of Rectangular Rapid Flashing Beacons(RRFBs), the Federal Highway Administration (FHWA) has issued eight official interpretationsto clarify the proper use, flash pattern, and luminous intensity of the device. The RectangularRapid Flashing Beacon, often used at pedestrian crossings, is a traffic control device used toenhance the conspicuity of the sign with which it is associated. This paper reviews these officialinterpretations and attempts to clarify the photometric terminology associated with the use ofrapid flashing beacons. Additionally, this paper uses the presented photometric terminology toinvestigate a relationship between the luminous intensity, the optical power (as defined by theSociety of Automotive Engineers), and the discomfort glare of rapid flashing beacons. As aninitial investigation, this paper finds that as luminous intensity and optical power increase, theodds of an observer indicating the device has unbearable brightness (discomfort glare) increases.Additionally, the data show that the odds of an observer indicating the brightness is unbearableare 13 times lower during daytime conditions than during nighttime conditions. These resultssuggest transportation agencies should focus on meeting minimum luminous intensityrequirements and put less emphasis on obtaining devices with the highest luminous intensitypossible. Additionally, these results suggest the profession should consider setting maximumluminous intensities for rapid flashing beacons.
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