January 4 – The Island Line, Isle of Wight temporarily closes for renovations and Class 483 units are withdrawn from service. The cars originally operated on the London Underground starting in 1938.
April 25 – Taichung MRT's Green line commences operation in Taichung. The line had opened the previous November, but was shut down for repairs after trains exhibited faulty couplers.
April 30 – Lastochka begins operating passenger services from Moscow to Minsk.
June 7 – 2021 Ghotki train collision: The Millat Express from Karachi derails near Daharki in Sindh province and the Sir Syed Express coming in the opposite direction collides with it and overturns, killing at least 50.
August 6 – The final section of the Delhi MetroPink Line between Trilokpuri Sanjay Lake and Mayur Vihar Pocket I opens after being previously delayed due to land acquisition and rehabilitation issues.
August 9 – The Tampere light rail system begins operation with Lines 1 and 3.