Police are investigating possible speeding as the cause of Thursday night’s rare tram accident after one of the passengers on board told them that it was swinging from side to side before it tumbled over, according to a source. Experts and tram drivers said that the experience of the 23-year-old driver, who was arrested yesterday, could also have been a factor when the tram crashed onto its side in Central, injuring 14 people. The driver, who joined operator Hong Kong Tramways last January, was arrested on suspicion of dangerous driving causing grievous bodily harm and later released on bail, pending an investigation. He must report back to police next month. Firemen and police were called to the scene shortly after midnight on Thursday after the tram No 123, bound for Shek Tong Tsui, derailed and flipped onto its left side on Des Voeux Road Central, near Bank Street, outside the HSBC headquarters. It took an S-shaped bend immediately before it crashed. A police source said a passenger had complained that the tram was going too fast for most of the journey and swinging from side to side before it crashed. This was one of the factors that led to the driver’s arrest. The source said a speed recorder installed on board the tram was being examined by the Electrical and Mechanical Services Department, and would be passed on to police next. Mechanical engineer and veteran traffic accident investigator Lo Kok-keung said it was common for trams to derail but in his decades-long career, he had never heard of a tram toppling over in Hong Kong. 14 hurt as tram topples over outside HSBC headquarters in Hong Kong’s Central district “It looks to be speed-related,” he said, noting the slight slope on the bend. “The high forces of inertia from a [high-speed] turn could have caused it to derail and tip over. Trams are very heavy and can weigh up to 19 tonnes. The bigger the mass, the higher the centrifugal force.” One tram driver with 20 years of experience said navigating the bend in question was not challenging but it was imperative for drivers to reduce speed before tackling it. “There is definitely a degree of danger because unlike other vehicles, trams cannot move freely; they rely on the tracks,” he said. “If I’m going down straight at 20km/h, I would reduce my speed by at least half or more before making a turn. Perhaps the driver did not have enough experience. It was very fortunate that no one was hurt too badly because there are usually a lot of people crossing the road there.” The last known case of a tram overturning was back in 1983 when a concrete mixer rammed into one in Shau Kei Wan, injuring 21 people. In 1964, a speeding tram overturned and toppled over at a double-bend in Admiralty, injuring 59 and killing one. The fact that the accident occurred at midnight – when there was less traffic and a higher speeding risk – could have also played a role. A former tram driver said most drivers at that time were on their last legs and rushing to the depot to clock out. “It’s usually a 10-hour shift with overtime,” she said. Hong Kong Tramways said it was fully assisting in the investigation. No problems were found during a maintenance check on the tramcar last month. A spokesman said all drivers received a mandatory eight weeks of training with at least six involving hands-on training with senior instructors on trams. The average age of tram drivers is 40. There were 34 road traffic accidents involving trams in 2016, compared to 38 in 2015 and 43 in 2014. The 14 victims, including the driver, aged 23 to 64, suffered minor injuries and 11 of them were sent to hospitals for treatment. Most were discharged yesterday. CCTV footage showed a double decker bus whizzing by at the time of the crash, but no collision was reported.