You might have guessed that San Francisco has twice as many hills in its city limits as does Rome, but did you know it also has one heck of a lot of tunnels? The reason, of course, is all those hills.
Tunnel-building is a longstanding tradition in San Francisco, but since the results are largely invisible, most people don’t know that as they walk or drive down a street they may be passing over a major hole in the ground.
San Francisco’s first major tunnel was the 1,000-foot-long Stockton Tunnel, opened in 1914 to carry four lanes of cars and buses under the edge of Nob Hill from the main business district to Chinatown and North Beach. It worked so well that tunnel building in San Francisco took on a furious pace.
In 1918 a streetcar tunnel over two and a half miles long under Twin Peaks, the City’s highest "hills," was opened from downtown to the outer Sunset District. When the surface streetcars on Market Street, the City’s main drag, were undergrounded in the 1980’s, the Twin Peaks Tunnel and the new Market Street Tunnel were connected to make a rapid transit tunnel over six miles long.
Ten years later another streetcar tunnel was finished. The Duboce or Sunset Tunnel carries streetcars under the northern edge of Mount Sutro from Market Street to the inner Sunset District.
In 1952 a 1,600-foot tunnel under Russian Hill, called the Broadway Tunnel for the street that runs through it, was opened to take cars and buses from North Beach to the Western Addition. The Broadway Tunnel was built by the Morrison Knudsen Corporation, which also built many major public works in the Bay Area.
After these successes car and bus tunnels were proposed everywhere, and some were even built. Tunnels carry six-lane-wide Geary Boulevard under Masonic Heights and a super trench takes Geary under Fillmore Street.
The granddaddy of all Bay Area tunnels was built in 1936 during the construction of the San Francisco–Oakland Bay Bridge. The bridge connects Oakland and San Francisco and was essentially a replacement for the extensive ferry system. The bridge is in two main sections, a double suspension bridge on the west end and a cantilevered bridge on the east end. These main sections meet in the middle of San Francisco Bay at Yerba Buena Island. San Francisco’s name before the gold rush was Yerba Buena (the "place of the good grass”; and the name was used for the island. To get the roadway from one side of the island to the other, the engineers dug a huge tunnel through the middle of the island. It is still the largest diameter, single-bore tunnel in the world with five lanes of traffic going each way, one above the other and each high enough for big trucks in any lane. Since the island is within the city limits, the Yerba Buena Tunnel qualifies as a San Francisco landmark.
The Golden Gate Bridge, finished at almost the same time, has its own tunnel. The Funston Avenue Tunnel takes traffic approaching the bridge under the picturesque San Francisco Presidio. On the other side of the bridge and thus just outside of San Francisco, Golden Gate Bridge traffic passes through the two Waldo Tunnels to reach the population centers of Marin County.
There are also railroad-only tunnels. Southern Pacific RR bored four tunnels between Third and Townsend Streets just south of San Francisco’s downtown and the south border of the City, over 8,000 feet long, in 1908. The Belt Line RR Tunnel, dug by the Harbor Commission in 1914, goes under Fort Mason on the north edge of the City.
There are even massive sewer tunnels. Since San Francisco collects all of its wastewater, including rain runoff for treatment and disposal, massive trench tunnels and holding tanks ring the City on three sides, picking up the waste water, storing almost 200,000,000 gallons at a time and transporting it to three treatment plants.
Perhaps the most amazing "tunnel" of all is the Bay Area Rapid Transit (BART) system. In San Francisco it bores deep under the City from the Ferry Building at the edge of the Bay to the Ingleside District, south of Twin Peaks. Down Market Street it runs in a tunnel UNDER the streetcar tunnel. At the Bay it dives from its tunnel under the dirt of the City into a steel and concrete tube over five miles long crossing under San Francisco Bay to Oakland. There it connects once again to a land tunnel under Oakland’s port facilities. BART trains cross through the tunnel in a matter of minutes from one side of the Bay to the other. When originally proposed, BART would also have bored under San Francisco’s hills to emerge near and cross the Golden Gate Bridge, but that San Francisco tunnel was never built.
One great thing about San Francisco's tunnels is that you can visit most of them on public transportation. For example, the 30 Stockton bus line runs right through the Stockton Tunnel.