When I lived in Phoenix, they had those. The leading left green arrow would be triggered when there were three cars or more waiting to turn left, otherwise you

When I lived in Phoenix, they had those. The leading left green arrow would be triggered when there were three cars or more waiting to turn left, otherwise you would get normal green that needs to yield to oncoming traffic and it usually took the entire light cycle for traffic to clear. The first car would stop at the normal line. The second car would wait a full car length behind and only move forward when a third car arrived. This way, you could trigger the "intelligent" light with only two cars instead of three and save yourself a full light cycle.