Intersection conflict warning systems (ICWS) are intended to reduce the frequency of crashes by alerting drivers of conflicting vehicles on adjacent approaches at unsignalized intersections, particularly those with one-way or two-way stop control. Few studies have explored the safety effectiveness of ICWS; the effectiveness has not been shown for four-legged intersections. This study sought to fill this knowledge gap. The full technical brief is available online at http://www.fhwa.dot.gov/publications/research/safety/15076/15076.pdf