Traswikied from http://lifeafterpeople.wikia.com/wiki/San_Francisco_Bridge
The San Francisco Bridge is a 137 m (449 ft) high and 812 m (2,664 ft) long cable-stayed road bridge across the San Francisco Bay in San Francisco. How long can it last?
1 Day After People: Across the world power plants fail, but when San Francisco goes dark the San Francisco Bridge stays on. Why? Because the bridge has atmospheric pressure controls which generate electricity from the towers top and bottom. So for now the bridge stays bright.
1 Year After People: Unlike the Hoover Dam the bridge still remains bright and will for years because the fuel is air. However the bridge itself remains as it was when people disappeared.
5 Years After People: The San Francisco Bridge has stayed on for 5 years. But now the generators which produce the electricity stop working because of a lack of maintenance. It takes the bridge over 30 minutes for the last light to go dark.
75 Years After People: 75 years without maintenance has left the bridge covered in corrosion. Soon a strong wind blows by, and just like Galloping Gertie, the San Francisco Bridge sways before the suspension cables snap, bringing the entire roadway down to the waters, the pull of the cables proves too much for the towers to withstand and they fall, and the San Francisco Bay is forever separated.