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A NEW LOOK AT OPTICAL SPEED BARS

On indoor roller coasters, riders perceive speed that has been manufactured optically, rather than by the actual speed of the ride alone. The perception of speed, rather than the actual speed, is what impacts the riders' thought and decisionmaking processes. The ride enhances the riders' perception of speed by providing a changing frame of reference. A series of lights appear with a consistent initial frequency, then appear more rapidly as the ride accelerates, exaggerating the sensation of motion. This concept has been applied to highway transportation in several contexts. One technique that utilizes this principle of perceived speed is referred to as optical speed bars (OSBs). OSBs are transverse stripes spaced at gradually decreasing distances with the intent of enhancing the driver's perception of speed, resulting in a speed reduction. Applications have been almost exclusively in situations where traffic traveling at highway speeds is required to slow to a stop or near stop, such as on a freeway exit ramp ending at a stop sign or traffic signal. Most formal studies have shown the technique to have significant merit, but do not agree on the mechanism by which the technique reduces speeds. This paper describes a test conducted by the Kansas Department of Transportation and the University of Kansas to determine the mechanism by which OSBs reduce speeds and to evaluate their potential effectiveness in highway work zones.