Key runway at SFO closing for 20 days, flight delays expected

FILE — Regional commuter jets land on parallel runways 28L and 28R at San Francisco International Airport in San Francisco, Calif. on Thursday, March 20, 2014. SFO will be shutting down Runway 28L for 20 days in September to reconstruct the base layer. less FILE — Regional commuter jets land on parallel runways 28L and 28R at San Francisco International Airport in San Francisco, Calif. on Thursday, March 20, 2014. SFO will be shutting down Runway 28L for 20 days ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 12 Caption Close Key runway at SFO closing for 20 days, flight delays expected 1 / 12 Back to Gallery

San Francisco International Airport is warning travelers to expect delays next month. A key runway will be closed for repairs between Sept. 7 and 27.

The delays are expected to be worse for short-haul flights (though all domestic and international flights could be affected) between Wednesday and Friday, which is the busiest part of the travel week.

To try and mitigate the problem, SFO has worked with airlines to reduce their flight volume by about 13 percent. But even with that planning, SFO is still anticipating delays between 30 minutes and 2 hours.

So if you're planning to fly out of the airport between Sept. 7-27, your best bet are early morning flights, as SFO anticipates delays will start after 9 a.m. during those 20 days.

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As disruptive as the work may seem, the airport insists it chose the September dates to avoid the busiest travel seasons during the summer and holiday season. Plus, they need weather to be dry, and September in the Bay Area usually isn't rainy.

The reason for the closure is construction of a new base on a 1,900-foot stretch of Runway 28L, which SFO explains is one of two runways at the airport used mostly for arrivals. The part of 28L being redone is where it intersects runways 1L and 1R, which are used mostly for departures.

"These runway intersections are the most heavily traveled areas of the entire runway system at SFO, with more than 68% of all flights crossing these intersections," the airport said in a press release.

This will be the second time in just over two years major work is being done on the runway; 28L was entirely repaved in spring 2017. It was during that resurfacing work that engineers discovered the base layer was showing signs of cracking, too. Now, those issues are finally being addressed.

According to the airport, the project is expected to cost about $16 million. It is federally funded.

Alix Martichoux is an SFGate digital editor. Read her latest stories and send her news tips at alix.martichoux@sfgate.com.