This information began as a snapshot of the interlockings that existed on the Great Northern System in 1935, including the Great Northern's Canadian interests. It now includes some newer installations as well. This is a work in progress and incomplete (as of 2015). By this time there had been towers and other interlockings built, modified and closed. Some of the locations listed have no closing date known to me (Peter Thompson). Some of these may have been closed by 1935.