United States Department of Transportation
i
Modern traffic control devices to improve safety at rural intersections.
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2011-12-01
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[PDF-4.19 MB]
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Abstract:"Engineers with the Texas Department of Transportation (TxDOT) frequently make changes to traffic control devices
(TCDs) to improve intersection safety. To use available funds judiciously, engineers make incremental changes in
order to select the least costly yet effective improvements. The goal of this project was to obtain a better
understanding of modern TCD capabilities. Researchers conducted the following tasks: literature review, crash data
examination, TxDOT district survey, laboratory survey, field study, and development of principles for selecting
TCDs. Adding flashing lights to signs, either through beacons or embedded light-emitting diodes (LEDs), serves two
purposes: to attract attention and to convey a message. The findings of this research demonstrate that while the lights
do improve detection distance, legibility distance of the message suffers at night due to the glare of the lights.
Cautious engineering judgment should be used when adding lights to any word message sign beyond a Stop sign
because the legibility distance for the words will be shorter than when lights are not present. For Stop signs, the
unique color and shape of these traffic control devices prompts drivers’ responses to them long before the word “stop”
is actually read. The driving study found no difference in sign detection at night between those with an overhead
flashing beacon and those where the ground-mounted sign has embedded LEDs. The detection distances observed for
the signs with lights in this study were extremely long, over 2000 ft in most cases. The other general observation
regarding the magnitude of the results is that for all of the Stop signs, both lit and unlit, the detection distance for sign
recognition was always greater than stopping sight distance. So the existing static Stop signs are sufficiently visible
for an alert driver under clear weather. The research project found that there appears to be a benefit to detection from
dimming the LED brightness at night. The LED sign set on the high brightness setting was detected furthest during
the day, while the lower setting was detected best at night. The research concluded with guidance principles to
consider when selecting countermeasures for rural stop-controlled intersections."
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