This is a parametric tramway, metro coach, or subway car depending on what you're looking for. You can modify its dimensions, number of doors and probably other things.
Its main feature is opening doors. It has sliding doors for the passengers and swivel doors for the driver and in the rear end of the coach. It is inspired by Kyoto tramway and St.Petersburg metro.
Please take a look at it in action: https://youtu.be/nTimVEHTe2U
With the default dimensions it's roughly the same size as typical Tomy trains, but it's not really compatible with plarail or Brio/Ikea.
The easiest parameter to modify is ndoors. I only tried printing with 2, but but try 3 or 4 or 20 ;)
Uses gear.scad 1.1 by Leemon Baird and parts of MCAD library.
There are several parts, some assembly required.
Everything except for the bogies, which are print-in-place with the wheels, prints without supports. Almost everything should be printed upside down so that it lies with the flat side on the build surface.
UPDATE: There are now separate bogies and two-part wheels. They print separately and roll much better than in-place. Print 2x bogie-bogie.stl, 4x bogie-wheelA.stl, 4x bogie-wheelB.stl.
The extra doors need to be split up (use Split in Slic3r) and oriented so that they lay flat side down.
The headlights, should you decide to print them separately, work best if you don't print the stem. Orient them so that they look up and slice the stem in Slic3r.
The top part/sliding doors mechanism
The door mechanism snaps together. Carefully insert both parts of the sliding doors, then the driving gear. Check that the mechanism works, then put the inner cover on the 4 connecting pins. Before doing that, make sure that the driving gear "axle" actually fits in and the gear still turns on it. It might be a tight fit due to some elephant foot effect.
Use a drop of CA glue to fix the headlights in place.
The bottom part
The bogies insert into the sockets in the top part and it's a very-very-very tight fit. If you're doing it for yourself, you probably don't need anything extra. If it's for your young train driver, probably secure them with a couple of screws. I used M2 screws, but the current STL files are updated for M3.
The driver's doors and walk-through doors
The 3 extra doors may require a bit of deburring in order to fit in the door frames and be able to open. Make sure that they open with a little bit of latching before final assembly.
Prepare 5 self-tapping screws of appropriate size. I cannot give the exact dimensions, but I'd guess they classify as "fairly small" in the general home improvement range of screw sizes. I used pliers to snap some thinner and longer screws so that their size is appropriate. First fix the two screws in the middle of the coach. Then proceed to insert the swivel doors and use the screws at the both ends.
Enjoy your tram! Please post a make if you print it.