Bench seats, smudged glass windows, folding or sliding doors, leather hand loops dangling from the ceiling, handrails, air vents, posters, ads, graffiti, slumped passengers carefully minding their own business by reading, texting, listing to music, playing games on a phone/iPod, torn cushions, litter on the floor, sliding doors between cars (on some), wet/dirty floor, lights, city streets flashing past the windows, security call boxes, buttons to open the door, signs to stay back from the door, speakers, people standing, sitting, hanging onto railings, newspapers left behind on the seat, groups of animated teens clustered together, train security, street people, gum stuck to the walls, burn or carve marks on the seat
The whoosh of air brakes, the scrape of a door sliding open, voice over the speakers announcing stops, creaks, snaps of electricity from outside, squeaks of rubbing metal during turns, voices, music from headphones, laughter, swearing, the rattle of a newspaper, zippers on purses/backpacks opening and closing, the rustle of plastic bags, the creak of fabric and leather as people shift position, coughing, throat clearing, street noise through open windows, a patterned thump, bells chiming a stop
Feet, body odor, perfume, body cologne, hair products, leather, greasy hair, dirt, cold metal, stagnant air, warm plastic
Gum, mints, coffee, bottled water, food grabbed from a vendor (although most people avoid eating on a train because it's so unsanitary)
Hard seats, the shaking side to side motion of rolling movement, brushing up against other people, bumping, knocking into someone unintentionally, squeezing past someone to get to the door, a cold metal handrail against the skin, clamping tight to a purse, backpack or bags, keeping an arm around small children or holding their sweaty hand in your own, pushing on a door with a sleeve or shoulder so you don't have to touch it with your fingers, holding bags on the lap so you don't have to set them on the dirty floor
--The words you choose can convey atmosphere and mood.
Anna slid closer to the window as a portly businessman sat down next to her, stealing all the space. He yammered non-stop into a cell phone, staining the air with onion breath so strong that most governments would classify it as a bio weapon. This is what I get for claiming the last empty bench on the train, instead of choosing a seat next to someone else.
The most peaceful ride into city center was always the Monday morning express train. No one jumped around, bopped to music or traded loud opinions about the big game the night before. Instead, glass-eyed travellers lined the seats in ordered rows, a carton of eggs ready for market.
--Similes and metaphors create strong imagery when used sparingly.
Example 1: (Simile)
The train stopped at the platform, its overheated brakes whistling like fireworks about to blow.
Example 2: (Metaphor)
After the rock concert let out, a mosh pit of shrieking teens poured onto the train, high on the buzz of music and whatever else had passed hand-to-hand through the crowd.