Traffic signals are timed to minimize stops and delay to all traffic using the intersection and “perfect synchronization” is rarely possible. Many factors contribute to the disruption of ideal progression: varying speeds, the presence of left-turning signals, the distance between signals, varying amounts of green time required by traffic on cross streets, and congestion from very high traffic volumes. Perfect synchronization for one direction of traffic on a street may result in frequent stops and delays for the other direction. A compromise that favors the heavier direction of flow is usually best.