The rollercoaster involved in a crash earlier this week is to remain closed "for the foreseeable future", Alton Towers has said.
Another similar rollercoaster, Saw, at Thorpe Park will also be closed while investigations are carried out.
A statement from Merlin Entertainments, which owns the theme park, said: "Since the accident at Alton Towers Resort on Tuesday afternoon Merlin Entertainments has been engaged in a thorough review and investigation of the events that led up to the incident and of its safety and operating processes. The investigation is ongoing and we are co-operating fully with the Health & Safety Executive.
"The safety of our visitors is our fundamental priority. We have a strong safety record at Alton Towers and across the Merlin Group. Today we are enhancing our safety standards by issuing an additional set of safety protocols and procedures that will reinforce the safe operation of our multi-car rollercoasters. These are effective immediately.
"Each rollercoaster has its own individual operating process and characteristics. Our central safety management team, together with local Park operations, will now work to implement and brief operating staff on these protocols. As a consequence, two rollercoaster rides have been withdrawn from service until the new safety protocols have been applied."
Emergency services work to free the trapped passengers from The Smiler ride
It has also emerged that emergency services were not called to Alton Towers until 11 minutes after the rollercoaster crash which left 16 people injured.
News of Tuesday’s accident reached theme park chiefs at 13:57 but ambulance crews did not receive a call until 14:08.
Although the West Midlands Ambulance Service arrived on the scene at 14.35, Alton Towers said that their “community first responders were on the scene within minutes”.
Fire crews were not initially requested but a call was put in by ambulance crews asking for assistance at 14.41 and the theme park itself at 14.45, according to the BBC.
In a statement, Alton Towers said: "Our community first responders, based on site at Alton Towers, are trained by West Midlands Ambulance Service and form part of our security and medical teams.
"Once the incident occurred, a member of the ride staff would have called our first responders who arrived at the scene within minutes.
"After instant assessment they call our security department who then call 999 straight away."
On Wednesday, a spokeswoman told The Huffington Post UK that ride staff and emergency services were on the scene "immediately" but it would have taken time to access the carriages, which are difficult to reach. She said that Alton Towers has its own response team which is medically trained and would have been on the scene within "seconds or minutes". She said she was confident that the teams responded "as fast as they possibly could".
Teenagers Daniel Thorpe, Vick Balch, Joe Pugh and Leah Washington were seriously hurt in the incident.
All are understood to have suffered serious leg injuries.
All 16 victims were stranded 25ft in the air at an angle of about 45 degrees for more than four hours.
The theme park remains closed while investigators examine the possible causes of the incident.
Leah Washington and Joe Pugh were among those injured
The £18 million rollercoaster, which boasts a world record 14 loops, has been closed twice because of safety concerns since opening two years ago.
Following the accident, Merlin Entertainments was the biggest faller on the FTSE 100, with shares down 3%.
The firm, based in Poole, has run Alton Towers since buying out previous owner the Tussauds Group in May 2007.