The Robin Williams Tunnel north of the Golden Gate Bridge is the portal into Marin County and beyond, and has a history as long as the span that opened in 1937.
The building of the Golden Gate Bridge was an engineering feat that opened up the Redwood Empire for economic growth and housing. But the tunnel also played a critical role. Initially one bore was built to handle two-way traffic when the span opened. In 1954 a second bore was added.
In 1970 rainbows were painted onto the south side of the portals on the order of Alan S. Hart, the former director of the San Francisco District of Caltrans, then known as the state Division of Highways. Hart was about to retire and made a last-minute decision to skip permission from his bosses in Sacramento for the paint work. He said the portal arches reminded him of rainbows. Initially top highway officials were angry, but calmed when the public embraced the rainbows.
Initially known as the "Waldo Tunnel," the structure was named after William Waldo, who was a Whig Party candidate for governor in the mid-19th century. The sections of highway to and from the tunnel are still known as the Waldo Grade. But when Williams died in 2014, the tunnel was renamed in honor of the actor-comedian in 2016.