Evaluation of Data from Test Application of Optical Speed Bars to Highway Work Zones

The proximity of traffic and workers in highway work zones demand that safety be a high priority. The issue of traffic speeds in highway work zones has long been an issue receiving much attention. Over the past three decades, many different measures have been developed to address the issue of speed in work zones. One that has garnered interest recently in the United States is the use of optical speed bars, transverse bars set out at gradually decreasing spacing in order to provide drivers with a heightened perception of speed. Studies have shown this technique to be effective at roundabout approaches and freeway exit ramps. This report discusses a test application of optical speed bars to a highway work zone. Accommodations had to be made for the unique characteristics of highway work zones. Simulations were developed to aid in visualizing the effects of various design parameters. The tested pattern comprised three components, a leading pattern of uniformly spaced bars, a primary pattern of bars with graduated spacings, and a work zone pattern consisting of intermittent groups of six uniformly spaced bars with large gaps between groups. The pattern was found cause reductions in mean and 85th percentile speeds, as well as in standard deviations. Changes in speeds were small, and resulted from both warning effects and perceptual effects. The warning effects persisted downstream of the pattern while the perceptual effects did not, as drivers increased their speed once out of the area with graduating spacings. Reductions in speed variations also persisted downstream of the pattern. The work zone pattern did not appear to have any effect on speeds or speed variations.