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Illinois State Police and IDOT Study on Warning Light Colors

The Illinois State Police and IDOT conducted research and published the results (2013) in their study: Effectiveness of Nighttime Temporary Traffic Control Warning Devices.  Some findings were predictable; others were unexpected.  The purpose of warning lights, across the board remains the same: to warn oncoming motorists that there is a problem ahead and to manage driver behavior when approaching and upon entering the targeted area.  The right color and configuration of warning lights on vehicles, particularly at night, can either save lives or jeopardize them as is shown by most recent research.

The purpose of the Illinois study was to identify shortcomings in their current practices and procedures, such as driver confusion, and to recommend improvements and guidance in the management, placement, and configuration of first responder and construction vehicle warning lights. Because of the immediate need to understand the full scope of emergency vehicle lights, their effect on motorists, and where they are needed, many states have conducted their own trials trying to understand the motorist/light color connection.  Thus far, there is still no national consensus regarding the use, display, and compilation of the results of that research; for some results verify what has been established before, some findings partially overlap, and some concentrate on aspects unique to that particular research.

Most studies found Amber Warning Lights to have some clear advantages over other light colors.

The Illinois Study used 100 volunteers who drove their vehicles at night from 11pm to 3am under rigorous guidelines in order to participate in the study.  And while subjective in nature, it offered valuable information about the cognitive perception of drivers in the early hours in a dark environment.   Each motorist was accompanied by 2 technicians; one measured the time of each encounter with a warning light color with a stopwatch, the other comments regarding when lights were seen and how they appeared.

White was seen first by all participants and at the greatest distance, but like so many motorists reported in other studies, the closer they got to the source the less they could see because of the extreme glare produced by the white light.  The interesting outcome from this study compares to the 1994 Phoenix Fire Department study that advocated turning off other colored lights when a vehicle was stationary and using only amber flashing lights.

The Illinois study went a step further, for it also recommended turning off other colored flashing light including white, but the IDOT promoted the use of amber directional lights (traffic advisor lights) by police vehicles instead of the rapid firing white/blue/red.  Drivers reported they felt less anxiety as they approached because the arrows told them what to do and how to proceed as they got closer and closer to the target area.

What is also an interesting comparison is that in the Kentucky report for road workers, the recommendation was to use large signs on top of slow-moving trucks with amber arrow directional indicators.  Again the test drivers reported feeling more secure because they knew what was expected by them when they saw amber flashing warning lights.

It appears that motorists feel better, are less anxious, and are more informed when they see a flashing amber arrow whether it’s on a light bar atop of a police vehicle or on a road placard.  Amber arrows communicate with motorists while random flashing red/blue/white lights leave them guessing.

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