Four O'Clock Factoid: Key to the System

Four O'Clock Factoid is a daily feature on Track Twenty-Nine helping to get you through the workday with a bit of useless knowledge.

When opened in 1936, the San Francisco-Oakland Bay Bridge was designed to carry interurban and light rail-type traffic, although trains did not come to the bridge until 1938. The lower deck of the bridge carried three lanes of traffic and two rail tracks; the upper deck carried six lanes of traffic. On the peninsula side, the Transbay Terminal was constructed for interurban and trolley traffic. Trains left the bridge on a looping viaduct which carried them above the streets of San Francisco into the terminal. When rails were removed from the bridge in 1958 in order to create two more lanes for cars, the Transbay Terminal and approach viaducts were reconfigured as a bus terminal - still in use today.