If you wonder what all those cryptic files in your installation folder are, here is a short explanation of them:

.geopcdx = is the 3D model itself and it's properties
.dscv = auto numbering selection list for rolling stock
.ban = Animated geo section
.lua = script files which control animations and other aspects of locomotives and signals
.TcPcDx = References the textures to the 3D objects from the the geopcdx and ban files
.bin = The blueprint file of any object in the game which contains properties, the name and other information and loads in all the above files to the game
.xml = raw format of the .bin files

.proxyxml = reference file for any sounds in the game
.proxybin = same as the proxyxml, for strange reason not used by the game

In some asset folders you will also see some .tga (picture), .psd (Photoshop), .ace (picture), .cost, .blend., .ia (3D building files) which are not required for the game and just have been forgotten by the object builders. Usually it is not safe to delete them.