Here is my rigged and animated inward sliding bus door which I made at work.
The door can simply be opened by one animation bone.
Modelled, rigged and animated in Blender 2.79b
Bus Door (1) Inward Gliding (Rig and Animation)
Test with city bus. The bus is still work in progress, there are some more detail I want to add. I think I will finish the bus this week.
Simple door control by one bone.
Demo Video (How the door looks in Blender)