Alton towers theme park has been closed whilst an investigation into a crash on their Smiler ride continues.
Four people were seriously hurt in the collision on Tuesday and were taken by helicopter to hospital.
Officials are trying to work out how the it happened and how to keep people safe in the future.
Merlin Entertainment, which runs the park, said: "The park will remain closed until we understand better the cause of this dreadful incident."
Rollercoaster crashes like this are incredibly rare.
The International Association of Amusement Parks and Attractions say that the chance of being injured on an amusement park ride is one in 24 million.