First test inconclusive but promising. I did a tour of various problem intersections, but other vehicles were present at most of them even waiting a cycle or two to see if it would clear. But there was one intersection I've never been able to trigger, that gave me an arrow when no cars were present. I'm going to have to get out very early in the morning to make multiple approaches with and without the reflector to see if it has any effect.

I noticed the sensors are in two different types of configurations. Pole mounted on the opposite side of the intersection pointing toward the traffic lane. And pole mounted on the same side of the intersection pointed downward at the lane. A single direction reflector might not work on that second type.