BART police arrested 27 people this week at San Francisco's Civic Center Station in a sting operation targeting narcotics users.
The three-day operation was conducted on Monday, Tuesday and Wednesday in response to complaints from riders and employees about drug user in the free areas of stations, according to BART.
"We want to send a clear message that drug use at our stations will not be tolerated," said acting Police Chief Jeff Jennings. "This illegal activity impacts our riders and employees as the users leave behind hazardous items."
Police used video surveillance cameras to identify potential criminal activity, according to BART officials.
Once plainclothes officers confirmed the activity, uniformed officers would move in for an arrest.
BART police said they are now working with the district attorney's office to build cases against the suspects.
The operation will be used to develop plans for a future joint operation with San Francisco police targeting criminal behavior including narcotics use in and around BART stations, officials said.