The incident occurred on June 2, 2015, on the "Smiler" rollercoaster at Alton Towers in the UK. The victim, Leah Washington (who was 17 at the time), was sitting in the front row of a carriage that collided at approximately 52 mph with a stationary, empty test carriage that had stalled on a low section of the track. The crash was the result of human error; engineers had manually overridden the ride's safety computer system, which had correctly identified the stalled carriage, because they mistakenly believed the warning was a "ghost" signal. The impact caused catastrophic "crush" injuries to the legs of the passengers in the front row. Leah Washington underwent a life-saving but traumatic surgery that resulted in the amputation of her left leg above the knee. Another passenger, Victoria Balch, also lost a leg due to the same collision. The park's parent company, Merlin Entertainments, was subsequently fined £5 million for health and safety breaches, and the ride has since been upgraded with redundant safety sensors.