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Transportation Research Board Abstracts

Response to Simulated Traffic Signals
Using Light-Emitting Diode and Incandescent Sources


John D. Bullough, Peter R. Boyce, Andrew Bierman, Claudia M. Hunter, Kathryn M. Conway, Akiko Nakata and Mariana G. Figueiro:

Abstract from the 2001 TRB meeting: Traffic Signal Luminance and Visual Discomfort at Night:

The visual discomfort from simulated traffic signals under nighttime viewing conditions was assessed. Discomfort increased with increasing signal luminance and with decreasing viewing distance. Color identification of signals was very high for all signal colors and luminances studied. Red signals meeting luminous intensity specifications of the Institute of Transportation Engineers (ITE) and specifications being drafted in Europe were unlikely to cause visual discomfort under the conditions tested. Green and yellow signals meeting the ITE and European specifications were more likely to cause visual discomfort. Dimming signals using light-emitting diodes might be a feasible strategy for minimizing discomfort under some nighttime viewing conditions.


John D. Bullough, Peter R. Boyce, Andrew Bierman, Kathryn M. Conway, Kun Huang, Conan P. O'Rourke, Claudia M. Hunter and Akiko Nakata

Presented at the 79th Annual Transportation Research Board Meeting, Washington, DC, January 9-13, 2000:

Simulated light-emitting diode (LED) traffic signals of different luminances were evaluated relative to incandescent signals of the same nominal color and at the luminances required by the specifications of the Institute of Transportation Engineers. Measurements were made of the reaction times to onset and the number of missed signals for red, yellow and green incandescent and LED signals. Measurements were also made of subjects' ability to correctly identify signal colors and of their subjective brightness and conspicuity ratings. All measurements were made under simulated daytime conditions. There were no significant differences in mean reaction time, percentage of missed signals, color identification or subjective brightness and conspicuity ratings between simulated incandescent and LED signals of the same nominal color and luminance. Higher luminances were needed for the yellow and green signal colors to ensure that they produced the same reaction time, the same percentage of missed signals, and the same rated brightness and conspicuity as a red signal at a given luminance. Equations fitted to the reaction time data, the missed signals data and the brightness and conspicuity ratings for the LED signals can be used to make quantitative predictions of the consequences of proposed changes in signal luminance for reaction time, brightness and conspicuity. Key words: traffic signals, visibility, light-emitting diodes (LEDs), standards.

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