The theme park boss whose record-breaking rollercoaster crashed, leaving four people seriously injured, said the troubled attraction suffered "teething problems" after opening.
Nick Varney, chief executive of Merlin Entertainments which runs Alton Towers, was speaking as the Health and Safety Executive continues to investigate why two carriages collided on the Staffordshire venue's new ride, The Smiler, yesterday.
A total of 16 people were hurt - including two men aged 27 and 18, and two women aged 19 and 17, who suffered serious leg injuries in the crash.
Alton Towers was closed today, with no timeframe on when it might reopen.
The £18 million rollercoaster, which boasts a world record 14 loops, has been closed twice because of safety concerns since opening two years ago.
In July 2013 it was shut after reports that a bolt was seen to have fallen from the ride and in November that year the rollercoaster was closed again after plastic guard wheels came loose and hit front-row riders.
Mr Varney described The Smiler as "a relatively new ride", and added: "All rides have teething problems when they open."
He said a fail-safe designed to prevent accidents like the one yesterday "didn't work the way it used to", which resulted in occupants being rescued from 25ft (7.6m) up in the air, at an angle of about 45 degrees. The ordeal for some lasted more than four hours, with the evacuation not complete until 6.35pm.
Mr Varney told BBC News that the two carriages "should not have been on the same piece of track".
He said: "Technically that should not have happened.
"Guest safety on those sorts of incidents is not really a major issue in the sense that when you're on a rollercoaster car, the car can't come off the track and you are restrained in the seats.
"When you have a glitch and the ride stops, it's not really an issue of safety to the riders.
"What happened yesterday is something that there are other fail-safes for. There are other braking locks that should stop two cars being on the same track, but that didn't work the way it was supposed to."
Theme park guests posted bloody images of the scene on social media yesterday after two carriages crashed on a section of its 50mph (80kph) ride.
A spokesman for the University Hospitals of North Midlands NHS Trust said one of the four seriously injured people admitted to the major trauma centre at Royal Stoke University Hospital has since been discharged.
Merlin Entertainments, based in Poole, Dorset, has run Alton Towers since buying out previous owner the Tussauds Group in May 2007.
Courtney Lucas, who was queuing with friends for the Smiler, said they were told there were "technical issues" with the ride and initially thought the people trapped were crash dummies.
She told the BBC Radio 4 Today programme: "My friends thought it was crash dummies in the ride because they weren't moving at first until somebody turned around and spoke to us. It was quite shocking.
"He was very distressed. He said 'Do you think this is funny?', because, obviously, my friend said the words 'crash dummies'. We just thought they really were.
"Once we got around the corner we could see there was a man who had blood on his face, there were people who were just very limp."
Others reported hearing "clanking" on the ride ahead of the crash.