Police said that too many people were driving too fast in wet conditions through the Caldecott Tunnel, causing a series of minor acidents that trapped nearly 100 people inside.
Two cars collided with a USPS mail truck, blocking traffic in the entire bore, which is 3,619 feet long.
Two hours after the motorists became trapped inside the tunnel, the two cars and mail truck were towed away.
It was unclear whether anyone was injured in the accident.