This is a snippet from http://www.cnu.org/highways/sfoctavia
After the 1989 Loma Prieta earthquake, the Central Freeway was rendered unsafe for driving. While the calls for its demolition had existed before this time, they had always been resisted as too vital for urban connectivity. It was argued that closure would surely result in unprecedented traffic jams. However, after the earthquake forcibly closed the highway, the congestion failed to materialize. This allowed for planners to seriously consider its removal.
Today, Octavia boulevard exists where the Freeway once stood. It's widely considered to be the reason why the Market/Octavia section of the city has improved considerably. It took a shock to the system to discover that the highway wasn't needed. A takeway: if a shock comes your way, make good use of it.