There is, however, a famous Tamil action film set on a train: (2017) — a real-life inspired cop thriller with a train sequence. But it's not "Chennai Express."
I think you might be referring to the 2013 Bollywood film starring Shah Rukh Khan and Deepika Padukone . chennai express movie tamil
However, that film is primarily in , not Tamil, though it is set against a Tamil backdrop (Tamil Nadu, especially the train journey to Chennai) and features several Tamil cultural references, songs, and dialogues mixed with Hindi. There is, however, a famous Tamil action film
If you are looking for a Tamil-language film with the same name, that film is primarily in