We enter a carriage that hangs from rails above. We’re welcomed on board and the train starts moving. Now and then it transitions to running on rails, and sometimes we have to hold on to handholds above us to pull us along the hanging monorail track. We are entering a void space, where we can’t see, but continue feeling ahead for the pulleys to pull our carriage along. It’s slow but we are doing it, hand by hand. Then, we crest a hill, and, back on our train tracks, we rattle out down into fresh air, trees and sunlight.

Proposed monorail between Seattle and Tacoma, ca 1911 (SEATTLE 751)

Trains are transporation which feels both historic and futuristic. From steam trains and mining trains to monorails and shinkansen, they span a huge imaginal width of human time. Trains take you places, and often, they take you to the same places repeatedly. 

Related to rollercoasters, which could be considered to be more dynamic, novelty trains, trains bring (sometimes dramatic) movement and change, or in the case of the commuter train, may represent habit and stasis in repeated patterns.
 
Trains can also appear as miniature or theme park railways, sometimes in holiday settings (in my experience at least), which is altogether a different type of train, yet still running on tracks, and still transportational for enjoyment or practical use.
 
If you’re dreaming of trains, where are you in relation to the train?
 
Are you in the driver’s cabin? The passenger area? Are you running to catch the train or waiting for the train to arrive? Are you passing through the train carriage from one platform to another? Or are you navigating the train station? 
 
What is the train station or train like? Are they clean, well lit, dark, graffitied… is the feeling interesting, rushed, routine? 
 
Are there people all around? Is it commuter hour, or is it a quiet time? 
 
If your dream starts in a train station or a train, we could say it is looking at part of your life that “is going places”, in a broad sense. The part of your life which takes you forward. For example, maybe this could be your career, your passions, your hobbies, it could be your drive for new experiences or preference for known habits. 
 
If one of these, or another, metaphor seems resonant, consider it in the light of the train in your dream again. If the train is part of your life that’s taking you “forwards” in some way, and you’re on a miniature railway by the sea, and in the dream you felt free… it’s a different picture to being the train driver where the signals fail and you suddenly have to brake at a rail crossing and the brakes don’t work.
 
Looking at your dreams metaphorically, do they paint a picture of something in your life with a similar feeling state to which the dream conjures? 
 
Usually dreams show us something new. For example, I might feel quite unsure in my career, but in my dream I’m the train driver’s assistant – and quite competent and valued. Your dream may be showing you another angle of your work you’d not considered.