Research performed to assess the effectiveness of a flashing warning-light system for use at work-zone lane closures is summarized. The system is composed of a series of interconnected, synchronized flashing warning lights that produce the illusion of motion. Researchers investigated motorist understanding and perceived usefulness of various designs of the warning-light system, and the potential of this system to yield significant operational or safety benefits in actual work-zone applications. Results from proving ground and field studies show that the flashing warning-light system used in the work-zone lane closure is perceived positively and is not confusing to the motoring public. The field-study results also revealed that the prototype warning-light system may encourage motorists to vacate a closed travel lane farther upstream from the work zone (which is believed to offer a potential safety benefit). When the warning-light system was activated at the urban freeway test site, a relatively new closure, there was a one-fourth reduction in the number of passenger vehicles and a two-thirds reduction in the number of trucks in the closed lane 305 m (1,000 ft) upstream of the lane closure. However, the system did not significantly affect lane choice at the rural road test site where the lane closure had been installed for 6 months. Thus, the greatest potential safety benefit of the warning-light system may be when it is used in conjunction with short-duration or intermediate-term maintenance or construction projects.