For the most part, major airports like San Francisco International avoid closing runways whenever possible. But on May 17, SFO will cut its number of active runways in half just as the summer travel season begins.

The reason isn't the low clouds that often slow air traffic at the Bay Area's largest airport, but rather the last phase of a $214 million project designed to bring SFO's runways up to federal safety standards. Airport officials insist the project will result in only minimal delays, but a looming deadline to complete the work means that the airport has little choice.

Safety first
During the four-month closure, the airport will install new Runway Safety Areas (RSAs) on both ends of Runways 1 Left and 1 Right, which are normally used for domestic departures. Nothing more than bare ground at a runway's threshold, RSAs are designed to give aircraft that overshoot the runway a cushion of space for coming safely to a stop.

The project is the result of legislation passed by Congress in 2005 that requires more than 40 of the country's largest commercial airports to have RSAs by 2015. SFO has already installed the safety zones on its longer pair of runways, 28 Left and 28 Right, which are mainly used for arrivals and long-haul departures to Europe, Asia, and Hawaii.