Towards the beginning of the film when Neeson's character is walking through Grand Central Terminal, there is a poster for Paddington 2, which shared its US release date with The Commuter on January 12th.
Neeson revealed on a talk show that no scenes were filmed on board an actual train. Instead, all of these scenes were shot on a soundstage, with the same single mock-up train cabinet serving as all of them, only slightly redressed, and all the outside scenery added in post production with the help of green screens.
Vera Farmiga (Joanna) and Patrick Wilson (Alex) co-starred as husband and wife paranormal researchers Ed and Lorraine Warren in The Conjuring (2013), The Conjuring 2 (2016), Annabelle Comes Home (2019) and The Conjuring 3 (2020).
When MacCaukey meets the Lt at the bar on his way home the Captain comes in (Sam Neill). He mentions that since his promotion to Captain he spends more time at City Hall than he does on the job, but that it 'goes with the stripes'. Captains and Lieutenants wear bars as signifiers of rank (Lt's wear a single bar and Captains wear two gold bars that look like a section of railroad tracks), only NYPD Sergeants have stripes. He should have said it goes with the bars (or with the rank).
The trivia items below may give away important plot points.
The film's plot bears similarities with Neeson's previous film Non-Stop (2014). Both films feature Neeson's character traveling; both characters are looking for a passenger who is hiding something that puts others in danger; they're both suspected by authorities to be the criminals themselves; they both save the day at the end of the films.
A major plot point is the search for a character named "Prynne," which, as MacCauley discovers, is derived from the Hester Prynne character in The Scarlet Letter (1995), which the character is reading. Captain Hawthorne's name is probably a reference to the man who wrote original novel - Nathaniel Hawthorne.
This is the second film to co-star Liam Neeson and Colin McFarlane, following Batman Begins (2005). This is also another film featuring Liam Neeson in which his character is stuck on a train about to derail and/or crash within roughly the last 30 minutes since Batman Begins.