The special New Year's Eve Flash Pass costs $6 and gets you unlimited rides on BART from 6 p.m. Monday, Dec. 31 to 3 a.m. Tuesday, Jan. 1. Riders with passes simply flash them to the BART Station Agent and pass through the swing gate. No need to use the fare gates! Passes go on sale December 10. Get your BART New Year's Eve Flash Pass at Safeway stores in the greater Bay Area, the BART Customer Services Center at the Lake Merritt BART station, or at MyTransitPlus Stores in the Embarcadero, Civic Center, Montgomery, Powell, Coliseum and Bay Fair stations.
Click on this pdf link for all the arcane locales to try and buy your BART "Flash Pass".