Annually, thousands of highway workers risk serious injury and death from drivers who enter work zones too
fast or accelerate after entering the zone and then, because of their excess speed relative to the environmental
limitations, have insufficient time to avoid accidents in the zone. Slow-moving vehicles are a problem in reducing
traffic flow. This research investigated the effectiveness of a system of pulsing lights, that gave the illusion of
movement (Phi phenomenon), in causing drivers to unknowingly synchronize their vehicle speed with the light
Forty drivers participated: 20 young (10 female, 10 male; 21-42 years) and 20 older adults (10 female, 10 male;
55-87 years). Each participant made 15 passes through the work zone: a control pass with stationary white lights,
two control passes with no lights, and 12 passes of test conditions -- 2 colors (red & green) x 3 apparent pulse
speeds (-80, 0, & +80 mph) x 2 zone entry speeds (40 & 70 mph).
Age, sex, and zone entry speed differences were found, but overall, (1) backward moving lights (-80 mph)
caused drivers to reduce their vehicle speed, (2) forward moving lights (+80 mph) caused drivers to increase their
vehicle speed, (3) stationary light and control lights had little or no effect, and (4) green produced stronger effects
than red. Backward moving lights caused the greatest slowing in the young while forward moving lights caused
the greatest acceleration in the old males and young females.
Vercruyssen, Max; Williams, Gayna; Wade, Michael G..
Lighted guidance devices: intelligent work zone traffic control.
Minnesota Department of Transportation.
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