Not much is known about these signals. The light would light upwhen a train wasn't around. It would go off when a train was approaching. The major problem was that the light would burn out, forcing people to stop, which of course, people never do, except for railfans, so that proved to be it's downfall, although with L.E.D. technology of today, these could make a comeback?
I do wish these wouldn't make a comeback. They just look too weird. This could work for private crossings......Maybe.