ProMods

I have recently become interested in doing some mapping and modeling for American Truck Simulator and I am curious what I should do to model the custom bridges I need. I think that you guys over here do this, so I am asking how would I either make it a prefab or actually properly bring it into the game when I am done modeling. Also some tips on modeling would be greatly appreciated. Thanks in advance.

You need to create the prefab in a software that has PMD support built in like Blender (Complex but Free) or Zmodeler3 (Simple but you need to pay)