Two roller coaster cars collided today at the Alton Towers amusement park just outside of London, in a terrifying realization of everyone's biggest theme park nightmare.
The incident occurred on a popular coaster called The Smiler, when a car packed with 16 passengers struck the rear of a second, empty car at roughly 50mph. According to eyewitness accounts, the ride was still in operation despite having been closed down earlier in the day due to technical problems, and both the occupied and empty cars had been held stationary before being seemingly switched back on and colliding with one another. Four of the passengers sustained serious injuries in the collision, and were evacuated to a local hospital via air ambulance shortly after they were removed from the ride.
Here's a frustratingly short (yet still troubling) video of the aftermath of the crash: