On May 12, 2015, an Amtrak train derailed in Philadelphia, PA, killing 8 and injuring 200 people. I saw a story on the incident where multiple NTSB spokespeople have said at this and other train derailments that Positive Train Control (PTC), had it been installed, could have prevented the derailments from happening, particularly in incidents where human error is the key factor, rather than technical failures or track obstructions. PTC uses GPS and transponder technology to avoid collisions and derailments by ensuring that trains operate within speed limits and do not cross improperly-switched tracks.
As the first link points out, the Rail Safety Improvement Act of 2008 (passed in the wake of the Chatsworth train collision) mandates that much of the nation's rail system have PTC installed by Dec. 31, 2015. However, the rail industry has been lobbying to extend the deadline, claiming that they will be unable to have PTC installed and operational on all required lines, and be forced to either cease operations, or operate illegally.
What is required to implement Positive Train Control on existing rail lines in the United States? Does implementation require track improvements, engine/car improvements, or both?
Are the systems that are currently used or in development inter-compatible? For instance, a commuter rail system near me uses existing BNSF and Union Pacific lines (among others) in addition to lines that it owns itself, and Amtrak operates on some of these lines as well. Do all trains operating on these lines need identical PTC systems, or can the commuter rail develop a different but compatible system than the freight rail?
How long have complete rollouts of PTC taken, and what have they cost? (This is a fact-based way of answering the more debatable question 'Is 7 years a reasonable period of time to allow for PTC development and implementation?' and to examine what kind of budgetary strain the unfunded mandate places on smaller rail systems.)