start/end , repeat and center pieces must go into the game as separated pieces. You must render them separately. So you need a LOD for each piece.
Once you have the scene with the completed bridge:
Start a new scene for the start piece, merge the complete model, center the start/end piece to 0,0 and make the LODs only for the start piece. (first model)
Open a second empty scene for the repeat piece, merge the complete model, center the repeat piece to 0,0 and LOD the repeat piece. (second model)
Do the same for the center piece (third model)
You should end with four different scenes:
1 with the complete bridge without LODs ( this will not be rendered)
1 with the start/end piece with LODs ( this will be rendered) - the piece (not the bridge) must be centered at X0,Y0
1 with the repeat piece with LODs ( this will be rendered) - the piece (not the bridge) must be centered at X0,Y0
1 with the center piece with LODs ( this will be rendered) - the piece (not the bridge) must be centered at X0,Y0
I hope this helps you to better understand to process
