A light-rail train that ran off the tracks, injuring 77 passengers, last week in Yuen Long was travelling at nearly three times the speed limit, black box records show.
The train had 150 passengers on board when three sets of wheels came off the track and three overhead line masts were damaged. Two victims remain in stable condition in hospital.
The driver had been suspended until the police finished their investigation, the MTR Corp said.
The company said it had submitted a report to the Transport Department and police. No mechanical fault was found.
A lawyer said the driver could face criminal charges for what was the most serious derailment since the transport system in the northwestern New Territories started operating 25 years ago.
On Saturday, transport minister Anthony Cheung Bing-leung said the firm could be fined as much as HK$15 million, under a new agreement with the government on a fare adjustment, for the interruption to services caused by the derailment.
Records showed the two-carriage train was travelling at 40.9km/h when it made a turn of nearly 45 degrees from Kiu Hing Road into Castle Peak Road, 2.7 times the speed limit of 15km/h on that section, said Dr Jacob Kam Chak-pui, MTR operations director.
"The cause of the accident is closely related to speed," he said, adding that the driver did not have any record of speeding in his two years' experience.
Kam said that unlike on heavy-rail systems, the driver controls the speed of a light-rail train. "A light-rail train works like any other vehicle. The drivers need to make impromptu judgments according to situations on the roads."
The train's maximum speed was 80km/h and it could travel at 70km/h at most on the network.
The MTR Corp said it would double the number of speed spot checks from the current 3,000 a year. It would also introduce a speed camera trial. Fewer than 10 cases of speeding were found every year, it said.
The train was assembled by a subsidiary of CSR Corp, the state-owned maker of the two trains involved in a collision in Wenzhou in 2011 that killed 40 people. Neither train was found to be at fault.
Lawyer Albert Luk Wai-hung said laws governing other vehicles also applied to light-rail trains, and the driver could face dangerous-driving charges. The maximum penalty is a fine of HK$25,000 and three years' jail. The MTR Corp did not face criminal liability but it was likely that victims would seek damages in civil cases, he said.
Yuen Long District Council discussed the matter yesterday. Councillor Kwong Chun-yu said MTR representatives did not give a satisfactory explanation.
The MTR Corp and the government would face queries from lawmakers tomorrow.
Ngai Kam-fai, chairman of the Railway Workers General Union, said speeding was rare.