The Dumbarton Bridge connects San Mateo and Alameda Counties, spanning the narrowest neck of San Francisco Bay, between Menlo Park on the west shore and Newark on the east. The present structure is actually the second Dumbarton Bridge. The original structure, the first Bay bridge for vehicles, was built by the Dumbarton Bridge Company for $2.5 million and opened in January 1927. It was a combination of truss spans and trestle, with a lift span of lightweight concrete. By the 1940s, growing volumes of traffic caused increasing congestion and safety hazards, creating the necessity for a new bridge. The state of California bought the bridge in 1951 for $2.26 million.
The new Dumbarton Bridge cost $74 million and opened in December 1984. Because of its location within the San Francisco Bay National Wildlife Refuge, special care had to be taken during construction to avoid disturbing the ecosystem's delicate balance. The span was built first, followed by construction of the approaches and the eastern shore's toll plaza. The bridge is 8,600 feet (2621.9 meters) long, constructed with steel box girder and pre-stressed concrete, and has a vertical clearance of 85 feet. The toll plaza has a covered walkway over the booths connecting the National Wildlife Refuge and Coyote Hills Park.
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