The plan was for color-coded protesters to possibly chain themselves to trains and shut down BART's busy evening commute.
The red team was the front line, representing a "high possibility of arrest," and all groups would text BART security positions to each other to monitor response times and coordinate actions over several stations for the Aug. 11 surprise demonstration.
It was such a serious threat that hours before the protest, in an emergency closed session, BART police briefed its board members of the threat and decision to terminate cellphone service for four hours.
In a three-page, open letter to its passengers and interviews Saturday, BART brass provided the most detailed glimpse into what led the transit agency to make its controversial decision to terminate cellphone service at its stations to thwart the possible protest.
"The overall information about the planned protest led BART to conclude that the planned action constituted a serious and imminent threat to the safety of BART passengers and personnel and the safe operation of the BART system," BART's interim general manager and board president wrote.
The demonstration never materialized, possibly because of the cut service, but the transit agency has spent the days since explaining its decision and responding to criticism that it compromised free speech rights and jeopardized rider safety by preventing emergency cell communication.
An international group of hackers targeted the public agency because of the move, and BART has been hacked twice. Another protest is planned Monday during the evening commute and the agency has not said it would rule out another cellphone blackout.
BART plans a special board meeting Wednesday to discuss the move.
The transit agency did not want a repeat of a July 11 melee, sparked by the July 3 officer-involved shooting of Charles Hill at the Civic Center station, said Bob Franklin, president of BART's board. During that protest, demonstrators held open train doors, climbed atop cars and mobilized the demonstration by hopping on and off trains, disrupting service to 96 BART trains, or two-thirds of the evening commute.
BART "intelligence" anticipated an escalation, according to the letter, "that could far exceed the protest of July 11."
"There was a high probability someone was going to get hurt," Franklin said. "The BART organization did not want to take that chance. If it's a choice between shutting off cellphone service and endangering the safety of our customers, the choice is clear."
BART board member Gail Murray, of Walnut Creek, supported the decision.
The protests "weren't peaceful nor were they intended to be peaceful," she said. "We were trying to protect the safety of our customers. It really was a dangerous situation. BART's core mission is to provide safe transportation to its customers. Cellphone service is provided as a courtesy."
BART maintained in its letter that protesters could lawfully demonstrate outside the train platforms, but overcrowded station decks could cause passengers to fall five feet onto the tracks and near an electrified third rail. The agency said 120 extra BART officers and personnel provided the needed emergency response capabilities Aug. 11, and riders could have used courtesy phones at stations or intercoms on each train car.
Meanwhile, riders at the Walnut Creek BART station Saturday had mixed feelings about the transit agency's letter to them.
"Granted they shouldn't be cutting off communication, that's not cool, but it's not worth stopping the entire BART system in San Francisco to get your point across," said Bill Abney, 30, of Walnut Creek, a BART commuter.
Charles Kilbourne, 56, of Vallejo, was frustrated with the protesters.
"So, these spoiled children should cry when they're told we're not going to play their game and let them disrupt other people," he said. "They think their rights were more important than everyone else's."
No one was envious of BART's position.
"More communication is better than less," said 43-year-old Mike Larkin, of Albany. "In hindsight, probably not such a great idea, but that's easy for me to say."
Reach Matthias Gafni at 925-952-5026.