I had a conversation with a BNSF track supervisor on Stevens Pass recently. I had noticed that concrete ties only 2 years old were being replaced. ( I camp often in this same location.) He told me that the type with the slide in clip & plastic shim have problems with the shims flattening out & allowing wide gauge. The metal & plastic shim used under the rail was also an issue. The new ties have a threaded steel insert; a lag bolt is used to hold a pretzel - shaped clip tight against the rail with no plastic used anywhere. Very European appearing, but it will become the new standard @ BNSF according to this supervisor.