That being the case it would seem to me to be possible to simply update the current MNR system by having a system that would dump the train before passing a stop signal, similar to the magnets used by Amtrak over the Cos Cob Bridge. The magnets would activate a mechanism that would dump the air before a stop signal is passed. A similar system could be used in working limit areas, with a mobile device that would do the same thing, only it could be controlled by the mobile unit remotely to allow trains through.
Overspeed derailments could be easily prevented by implementing a more extensive use of a LIRR style ASC using multiple frequency pulse codes, and adjusted signal blocks.
In an ideal world, this would be my choice. It's combining two well proven technologies. Passive beacons could eventually be backfitted in high traffic areas to provide 'hinting' to the on-board computer to create a protection 'envelope' for the train. None of this is exotic.
And, maybe, if the industry proposed and moved in this direction 20 years ago, we wouldn't be here talking about it, today. IMHO, industry inaction, combined with a wish list from the NTSB, etc, that started growing, lead to today's PTC mandate.
One problem I see would be train to train collisions and main line switches not properly lined. First improperly lined switches: MNR's current system forces trains to approach open switches at restricted speed. Furthermore HTEL switches cannot be opened without several requirements. MNR cannot actually stop a train from going through a misaligned switch, hopefully being on a restricted cab would indicate to the engineer that something is amiss.
Again, in an ideal world, I don't see this being a huge issue - that's what restricted speed is for in the first place (!).
According to FRA requirements that's not good enough.
See above commentary as to how it got that way. IMHO, the industry painted itself into the corner its in. Whoops.
Being a computer programming major in college I could even program such a system. It's not that difficult. The thing that concerns me is the use of GPS in controlling train movements. The code only works if the proper coordinates are inputed and commercial GPS is just not accurate enough in my estimation to provide that reliable and consistent input into the system.
I generally don't trust GPS systems any farther than I can throw them...
Of course, the old-timers felt the same way when they took out the waysides and put cab signals in.
The TGV goes a step further than Metro-North - there are no wayside signals on LGVs, period. Only signs to mark where blocks end. I don't know if TVM enforces stops (though it can tell you there's one ahead)