The main reason for spending mega-billions of dollars on underground rail has been shot down. An environmental review finds that in 2035 the planned subway extension will result in only a 1 percent reduction in automobile use, and that the San Diego Freeway, the Santa Monica Freeway and the major streets along the line will remain heavily congested. From the LAT:

"Remarks that transit relieves traffic congestion are common, but they are without a factual basis," said Tom Rubin, a transportation consultant and former transit agency executive in Southern California. "The roads in Los Angeles are so far over capacity, it is difficult to get improvement from new transit projects."

While there's obviously a lot more to the report, the whole point of having a subway is reducing congestion. If that's not going to happen, why bother? I would suspect the community groups who are raising concerns about subway construction are going to have a field day with this.