A group of kids in eastern Marin County, California, was playing with an e-bike on a warm Saturday night in 2023. Amelia Stafford, who was 15 at the time, got on the bike behind someone and rode up and down the street, Coral Billisi, Amelia’s best friend, recalled. Coral said it was such a short ride that wearing a helmet didn’t occur to anyone. When the bike toppled over, “our immediate reaction was that we all started laughing — we just thought it was so funny,” she says. “Like, Ha ha, they’re so stupid, they can’t even ride bikes.” Then they saw the blood on the pavement around Amelia’s head. Before the crash, Marin County officials had needed hard numbers to effect a change in public policy. But then, said John Maa, a chief trauma surgeon who was on call that Saturday night, Amelia crashed, and everything changed: “It was like a light switch.” Photo by Balazs Gardi for The New York Times #ebike #emoto #MarinCounty #California