The Bay Area Rapid Transit (BART) District, serving the San Francisco area, has an obligation to protect its riders, wrote Grace Crunican, BART's general manager, in a Monday filing to the U.S. Federal Communications Commission. The FCC has been investigating BART's three-hour in some of its San Francisco stations last August in an attempt to disrupt a planned protest.

Mobile devices can be used to detonate explosives, . "BART is concerned ... that it must have the tools at its disposal to protect that public from wrongful use of wireless devices, as they can be used as an instrument for doing harm to passengers and BART employees," she wrote. "A temporary disruption of cell phone service, under extreme circumstances where harm and destruction are imminent, is a necessary tool to protect passengers."

Crunican, in her comments to the FCC, included BART's mobile service interruption policy, which allows the agency to disrupt service when there is "strong evidence" of imminent illegal activity that threatens public safety, the destruction of BART property, or the substantial disruption of transit services.

However, several digital rights groups disagreed with BART. Blocking mobile phone service in an emergency may actually compromise public safety, as well as free speech, eight digital rights groups told the FCC in their own filing. There are no examples where a mobile service shutdown would result in more benefits than harms, said the groups, including Public Knowledge, Free Press, the Electronic Frontier Foundation and the Center for Democracy and Technology.

"Deliberately interrupting wireless service, in nearly all cases, will mean disrupting the communications of every person in the affected area," the groups said in a . "Unlike the disconnection of a wireline connection, which can target an individual telephone facility, wireless interruption will necessarily prohibit the communications of completely innocent parties -- precisely those parties closest to the site where the emergency is located or anticipated."