The likelihood that a completed high-speed rail line in California would instantly become a top terrorist target was obvious to me five and a half years ago.  You can read it here.  I was pleased to see the Mercury News run a piece by a retired L.A. sheriff named Jerry Harper who writes

Protecting a train hurtling 220 miles per hour on more than 800 miles of track is a different story.  Should we build a fence around the train? Is it possible for security to be omnipresent via helicopter and ground surveillance? Will the government create a huge police force just to protect the rail system? I haven't seen many people asking these tough questions, but they need to be asked.  

Protecting the system could cost far more than anyone has anticipated.

If terrorists are able to derail the high-speed train, causing hundreds of deaths and injuries, the cost would be devastating, immeasurable and would never be offset by future passenger fares. An attack on a train that holds hundreds of passengers traveling at such speeds and that costs billions of dollars would create an international media bonanza for any terrorist group, foreign or domestic.

Sheriff Harper is correct, but only goes half way to understanding the full problem.  Protecting the tracks is nigh impossible as he notes, but protecting the stations and the waiting passengers is even harder since there are no provisions for the space, equipment or manpower that would mimic the TSA checkpoint at an airport.  You read it here first; in November 2010.  If completed, HSR is a disaster waiting to happen.