The name Dumbarton floats across the bay from Scotland, bestowed in 1876 on a point of land near the bridge's eastern terminus. The original bridge opened on January 17, 1927, making it the first vehicular crossing of San Francisco Bay, predating the Golden Gate by a full decade. Built with private capital, that early span was a two-lane drawbridge with a lift section for boats. The state purchased it in 1951 for $2.5 million. A portion of the old drawbridge still extends from the eastern shore as a fishing pier, its concrete pilings weathered by decades of salt air and tidal surges.

At the bay's narrowest southern reach, the Dumbarton Bridge stretches as the shortest highway crossing of San Francisco Bay. More than 70,000 vehicles traverse it daily, along with roughly 118 cyclists and pedestrians on weekdays and 384 on weekends, using the dedicated path along its southern edge. The current bridge opened in October 1982, a high-level structure built north of its predecessor. Twin steel trapezoidal girders carry the center spans, while pre-stressed lightweight concrete supports the approaches. Power lines run parallel to the roadway, marching across the water like sentries guarding the passage between Fremont and Menlo Park.

The bridge lands in the heart of contrasts. To the west, the tech campuses of Facebook and Oracle sit within commuting distance. To the east, the Don Edwards San Francisco Bay National Wildlife Refuge spreads across salt ponds and levee trails, home to the endangered California clapper rail. The Hetch Hetchy Aqueduct runs between the vehicle bridge and its abandoned rail cousin, emerging from underwater to cross the bay in plain sight. Coyote Hills Regional Park rises north of the eastern terminus, and the Alameda Creek Regional Trail winds from the bay to Niles Canyon, offering escape from the concrete arteries below.

Just south of the highway bridge lies the Dumbarton Rail Bridge, built in 1910 and unused since 1982. Its western approach collapsed in a 1998 fire, and the swing span now rests permanently in the open position, a rusting monument to abandoned ambitions. When trains still ran, boaters would signal the operator, who would start a diesel engine and rotate the bridge on a massive gear. Plans for commuter rail service linking the Peninsula to Fremont have circulated for years, but in 2008, $91 million earmarked for rehabilitation was redirected to the BART Warm Springs extension instead.

The original 1927 bridge charged 40 cents per car plus a nickel per passenger. Today, westbound drivers pay $8 at electronic tolling stations, with rates scheduled to climb to $10.50 by 2030. The transformation from human toll collectors to all-electronic payment accelerated during the COVID-19 pandemic in March 2020. The old toll booths stand empty now, awaiting removal to create true open-road tolling. In 1971, the film Harold and Maude captured Maude speeding through the original toll plaza, disobeying a police officer in a scene that preserved a vanished crossing for cinema.