Sliding doors are one of the design problems that featured in the LEGO Tangara MOC.

The doors "pop" out together, then slide apart.

There are a few forces at play here:

1. A brake is in place to stop the doors accidentally opening due to inertia when the train rounds a corner. Push the brake open by tilting the lever on the roof.
2. Both doors are held in place attached to a sliding axle. Hold the door rail and pull outwards.
3. Each doors slides individually across the axle. Hold each door rail and slide them to the side.

I went through a few iterations on the doors, finally happy with these ones. A good amount of rigidity (they don't fall apart when played with) and stability (they don't open by themselves when the train moves).

If you have any feedback or questions related to this article, please reply to my post on Mastodon. This article is part of the LEGO set.