Using AS for smooth motion tween - decelerate to stationary

Bit of a newbie with ActionScript, so apologies :be:

I have an icon of a railway train which pulls into a station. At the moment it is a motion tween, and I have had to edit every few frames, modifying the train’s position, so that it slows down as it enters the station.

This is messy, and time consuming.

Is it possible for someone to give me guidance on how to slowly decelerate an object? The train is almost isometric, so doesn’t actually move horizontally; but “south-westerly” across the landscape:

Any thoughts much appreciated!