How do I get there if I get off at Powell? Or is there a closer station to Ocean Beach? Thanks 
I’m starting from the Union City station. So I should get off at Civic station, and then go outside to the MUNI? I hardly go to SF, and I usually only go on the BART.
Get off at Civic Center, then transfer to MUNI N-Judah for Ocean Beach from the same station. BART always comes in on the Lower Level of the station. And MUNI uses the Mezzanine Level. The destination signs on the trams will say "Ocean Beach" because it is the last stop.
Edit – Do not go outside at Civic Center. Simply get out of the paid area for BART and find the MUNI gates. Feed $2.00 worth of coins into the slot – there are change machines nearby if you only have bills – and head down to the MUNI platform. The gate will spit out a transfer slip, which you should keep in case you run into San Francisco’s finest. The economy is bad and they have been ordered to vamp up fare evasion enforcement on MUNI. The fine for getting caught without a transfer are $75.
Get off at Civic Center, then transfer to MUNI N-Judah for Ocean Beach from the same station. BART always comes in on the Lower Level of the station. And MUNI uses the Mezzanine Level. The destination signs on the trams will say "Ocean Beach" because it is the last stop.
Edit – Do not go outside at Civic Center. Simply get out of the paid area for BART and find the MUNI gates. Feed $2.00 worth of coins into the slot – there are change machines nearby if you only have bills – and head down to the MUNI platform. The gate will spit out a transfer slip, which you should keep in case you run into San Francisco’s finest. The economy is bad and they have been ordered to vamp up fare evasion enforcement on MUNI. The fine for getting caught without a transfer are $75.
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You don’t need BART. The streetcar on Market Street called the "L Taraval" train goes all the way there.
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Take N judah going straight to ocean beach.
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Market and Powell then take bus.
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Where in Ocean Beach do you want to go?
Take BART from Union City to Powell or Civic Center Station (it doesn’t matter which one). Go up one level (not outside) and take either the N-Judah or L-Taraval Muni Metro streetcar line to the end. Or, exit the station onto Market Street and catch the Muni 71-Haight/Noriega bus. The N goes to Judah Street, the L goes to Taraval Street (and the SF Zoo), and the 71 goes to Noriega Street. If you’re not sure which one you want, I recommend the N-Judah because it runs near Golden Gate Park.
Powell Station is located in a nicer area than Civic Center Station, so I suggest using it instead. Powell Station is connected to the San Francisco Shopping Center, so you can stop for food and a restroom break if you like.
References :
http://www.sfmta.com