High occupancy vehicle (HOV) lanes in California were studied to see how well they reduce traffic congestion and save travel time. Researchers looked at different types of HOV lanes in various regions and compared their performance before and after changes were made. They found that HOV lanes with continuous access in Northern California and buffer-separated limited access in Southern California both help relieve congestion and increase highway capacity. The study also used traffic flow diagrams to measure how well the lanes were working.