Evaluation of Roadway High-Mast Tower Lighting

This study conducted an evaluation of high-mast roadway lighting, which included a review of Illinois Department of Transportation’s high-mast lighting specification and a field experiment. The lighting specification was reviewed for potential cost-saving measures. Recommended changes included the use of an external drive mechanism, a design-by-application mounting ring, and using the industry standard handhole design. The field experiment consisted of two human factors evaluations. In one evaluation, participants were driven along I-57 through five interchanges with various lighting designs and answered questionnaires about the lighting. Results showed that interchanges that were fully lit outperformed partially lit interchanges for perceptions of comfort, safety, and visibility regardless of whether the interchange used conventional lighting or high-mast lighting. When comparing participants’ responses between high-mast lighting at full intensity or at a 50% dim level, there was no change in perceptions of comfort, safety, or visibility. In the second evaluation, radar sensors were placed at key locations at each interchange and the speed behavior of traffic was recorded and analyzed. Speed analysis showed that lighting designs using only high-mast lighting had a potential ±safety benefit via reductions in vehicle speed variation. Comparing high-mast lighting at full intensity and at a 50% dim level, the dimmed lighting resulted in a significant reduction in speed for exiting traffic. Furthermore, dimming improved safe speed behavior on ramp segments while not significantly affecting the speed behavior for vehicles traveling through the interchange. Recommendations based on the results include using full interchange lighting designs, using a single light type (conventional or high mast, but not both), using a lower light level, and dimming lighting during times of low traffic volume.