The RAIB report, published on 7 December 2017, also makes 15 recommendations to improve safety and prevent similar incidents in the future.
Seven people were killed in the incident on 9 November 2016 and a further 51 were injured.
The tram was found to be travelling well over the recommended speed limit when it approached a bend at Sandilands Junction and derailed.
The seven passengers who died were thrown from the tram through windows and doors. The other passengers told the RAIB that they were thrown around “like being in a washing machine”, and were then left trapped inside with no obvious means of escape and no emergency lighting. They eventually managed to smash the front and back windscreens to create an escape route.
Inquests into the deaths of the seven people who died are due to be held in 2018, when all issues regarding the immediate cause of the crash and any systems failures leading to the crash, will be considered.
The RAIB’s safety recommendations include analysis of whether passenger containment by windows and doors could be improved, a system to automatically slow trams approaching high risk locations at speed, installation of emergency lighting and a review of operational risks and control measures relating to tramways.
“We welcome the investigation by the Rail Accident Investigation Branch which has provided some answers about the crash to the victims and their families.
“We hope that the recommendations from the report will be implemented as quickly as possible to improve safety for all passengers across the tramways in the UK.”