London - The operator of a British theme park where a rollercoaster crashed earlier this week, seriously injuring four people, said Friday it had closed three rides at other parks.
A total of 16 people required medical attention after the carriage they were in hit an empty carriage on The Smiler ride at Alton Towers, in central England, on Tuesday.
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The resort has been closed since then and another similar ride, Saw, at Thorpe Park west of London, was also shut down following the accident.
Merlin Entertainments, which runs both parks, said The Smiler and Saw both made by Germany company Gerstlauer would remain closed "for the foreseeable future".
The firm said it had also introduced new safety protocols across all its rides, and two rollercoasters at a third park, Chessington World of Adventures, were temporarily closed while these protocols were implemented.
"This has been a terrible experience for everyone involved and one we sincerely regret," said Nick Varney, chief executive of Merlin Entertainments.
Two of the four people who suffered serious leg injuries in the crash, were reportedly teenagers on a first date.
"It is an accident that should not have happened, and we are determined that it will never happen again," he said.
"Whilst the investigation into the causes is continuing, we have identified a series of additional safety protocols that we are implementing immediately across our multi-car rollercoasters."
The Smiler opened in 2013 and is billed as the world's first 14-loop rollercoaster. The Alton Towers website said the ride is "not for the faint-hearted".