The comic this film is based on doesn't make a huge amount of sense. The film probably even less so.
It strives for deep allegorical meaning but doesn't really make it.
It does work much better however as a satirical, often quite farcical take down of Ayn Rand (who certainly loved her trains). Literally children are used as parts of a machine to keep society going. Don't think about how it makes no sense at all, here's a pointless fight scene to cover up the cracks.
Tilda Swinton exemplifies the archly funny end of the film's wildly varied tones. Hilarious as a petty bureaucrat, looking like she is ready to run a Church fete whilst ordering how many people should die. The name of John Hurts character - Gilliam, a possible indicator of some of the tone they were aiming for.
Chris Evans is much less ably used, a naturally charismatic and interesting performer the role is too dour to make use of his talents and everyone around him seems much more colourful.
Well shot making good use of switching between the tight messy tail section and various other carriages it remains a quirky fascinating movie despite it's flaws.