Why? Because the major car route from the East Bay to San Francisco was closed and residents know how awful it is to be stuck in back ups on the other routes which are for the most part also bridges.
Just more evidence that people will use mass transit when it's a more attractive option than driving.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/09/05/BA8ORV1MN.DTL&hw=BART+record&sn=002&sc=842BART set ridership records each day of the holiday weekend as thousands of Bay Area residents and tourists rode its trains during the 70-hour closure of the Bay Bridge, transit district officials said this afternoon. The system carried 389,400 passengers on Friday, when the bridge was closed to traffic at 8 p.m., breaking the previous weekday mark of 381,200 set on June 13, the day of a concert by the Police at the Oakland Coliseum and a Giants' home game.
On Saturday, the transit system logged a record 278,600 passengers, including thousands of fans going to Berkeley for Cal's football game against Tennessee. The previous Saturday mark was 229,600 riders on March 3, the day of the Chinese New Year's parade.
BART also cracked its Sunday ridership record, with 208,700 riders on a day that included an afternoon free concert at Golden Gate Park to celebrate the 40th anniversary of the Summer of Love in San Francisco, officials said today. The Sunday record had been 195,700 on June 24, when many riders took BART to the gay pride parade in San Francisco.
In addition, 21,100 people rode BART overnight during the weekend - 6,900 between 1 a.m. and 6 a.m. Saturday, 9,900 between 1 a.m. and 8 a.m. Sunday and 4,300 between 1 a.m. to 6 a.m. Monday.
The last stats, overnight ridership, are significant because normally BART is shut down during those hours and there is endless debate about whether that should change. I hope that this experiment helps the operators move forward towards a 24 hour system.