Along these lines, there was just an interesting latimes article a couple days ago about a subway tunnel currently being bored in downtown LA which provides som

Along these lines, there was just an interesting latimes article a couple days ago about a subway tunnel currently being bored in downtown LA which provides some insight into the current process: http://www.latimes.com/projects/la-me-metro-tunneling/ http://www.latimes.com/projects/la-me-metro-tunneling/