The San Mateo - Hayward Bridge (commonly called the San Mateo Bridge) is a bridge crossing California's San Francisco Bay, linking the San Francisco Peninsula with the East Bay. The bridge's west end is in Foster City, the most recent urban addition to the eastern edge of San Mateo. The east end of the bridge is in Hayward. It is the longest bridge in the San Francisco Bay Area and the 25th longest in the world by length. The bridge is owned by the state of California, and is maintained by Caltrans, the state highway agency.
The bridge is part of State Route 92, whose western terminus is at the town of Half Moon Bay on the Pacific coast. It links Interstate 880 in the East Bay with U.S. Route 101 on the Peninsula. It is roughly parallel to and lies between the San Francisco – Oakland Bay Bridge and the Dumbarton Bridge, and is sometimes used by commuters to avoid traffic delays due to emergencies on those bridges.
The original bridge, known as the San Francisco Bay Toll-Bridge, opened in 1929 and was then the longest bridge in the world. The original bridge was mostly a two-lane causeway with a 300-foot (91 m) vertical lift span over the main shipping channel. The bridge originally had pole lights along the entire stretch, which were later abandoned except over the vertical lift span. It was replaced with a modern span in 1967. The total length of the bridge is 7.0 miles (11.3 km). The 1.9 miles (3.1 km) highrise section, the western end of the bridge, is composed of multiple steel girder spans. The eastern trestle portion accounts for the remaining 5.1 mi (8.2 km) of the overall length. The shipping channel beneath the highrise is 750 feet (229 m) wide with a vertical clearance of 135 feet (41 m). The bridge recently underwent an extensive seismic retrofitting to protect against earthquake damage. The bridge carries about 93,000 cars and other vehicles on a typical day.