I looked at a map and it looks like SFO is quite far from San Francisco proper. I'm just traveling by myself with only a small suitcase and would prefer to take public transportation over a cab to save money. Are there any buses or trains that will take me there?
BART! It's the SF Bay Area's subway system (stands for Bay Area Rapid Transit), and it will cost you less than $10 to get you from San Francisco International Airport (SFO) to the city, depending on which station you get off (it's currently $8.25 to get downtown). If you're going to Downtown San Francisco, wherever you're headed is likely close to one of three BART stations -- either Powell St. BART Station, Montgomery or Embarcadero. You can pretty much walk anywhere downtown from a BART station and worse case scenario is that you have to hail a cab for a short ride once you get there (which is really easy to do Downtown).
The SFO BART station is at the International Terminal, so just follow the signs that say AirTrain or BART. From any other terminal, you could also walk there, but it'll be faster for you to take the free AirTrain (just 1-3 minutes versus a 10-15 minute walk). Just follow the signs to AirTrain and hop on the red line. Once you arrive at the stop for the BART station, just head downstairs and follow the signs to the BART station (you'll see it right away).
Here are more specific details from the official BART website, 'The BART station at SFO is located in the International Terminal. It's a short walk from United Airlines in Terminal 3 and a slightly longer walk from Terminal 1. You can also take the free AirTrain from both terminals directly to the BART station. Just follow the signs to AirTrain and board the Red Line train. When you arrive, take the escalator down to the departures level and walk straight ahead to the BART station. Terminals 1, 2 & 3 are approximately a one to three-minute AirTrain ride to the BART station.'
If you're staying a little further than Downtown, you can also look into shuttles. There are plenty of kiosks at SFO that can help accommodate you.
By the way, bear in mind that depending on the day, BART operates from around 4'ish AM to around 12:30-1 AM (Check their website for a more accurate schedule: bart.gov). Most people don't have an issue with early flights, but some people may have issues with flights that come in very late.
If you do happen to miss the last BART train, take a shuttle or flag down a cab on the curbside. The upside when you get in that late is that there will likely be no traffic.
Enjoy SF! :)
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I go to San Francisco pretty often for work and fly into SFO. Even though I can expense everything, I still try to go the BART route because it's fast, and hassle-free, plus bonus points for saving my company money and being able to get some reading and work done during the ride.
There have been a couple times when I got in ridiculously late and the subway wasn't running anymore, so I had to take a cab, which is about $50 + tip to Union Square.