Commuters around the world would be understandably rattled by the deadly blast by a homemade device on a subway car in St. Petersburg, Russia. Statistically rare, terror attacks on public transportation—such as the March 2004 train bombings at Madrid’s Atocha station, the July 2005 attack on the Underground and a double-decker bus in London, the…

via What makes mass transit so great is exactly what makes it so vulnerable to attack — Quartz