By Garrett Leahy, George Kelly, and Joel UmanzorUpdated Feb. 13, 2024 • 6:32pmPublished Feb. 13, 2024 • 5:00am. Two teenagers died after falling from trains in San Francisco in the past two weeks. Now, their grieving mothers are sounding the alarm about a dangerous trend of young people climbing onto the top of BART trains and “surfing” them, and posting stunt videos on social media.