Ideally we should look to Europe and Asia for PTC. Almost all EU countries have PTC installed on their entire networks and these systems are all inter-operable. The TGV, Eurostar, ICE, and Thayls all operate on different PTC systems in international service and these systems have been in use since TGV's first appeared. The system used in The UK on Network Rail has been around since the 1970s after it replaced an older system that was first installed in the early 1900s. Why can we take one of these systems and adapt it for use in America? There's no need to re-invent the wheel to install PTC.
I feel I need to correct some mistkaen impressions that are being created here.
At least UK does not have PTC except on HSR-1, which has TVM430 (and possibly one or two other segments with very recent installations - i.e. post 2005). UK regulations do not require PTC for operation at 125mph. TWS is enough per UK regulations. Also the PTC systems used on HSR lines are not available on the upgraded Classi lines. Those still run with the traditional cab signaling systems.
Most Europe classic lines have cab signals, many also with ATS, but not necessarily PTC. And each EU country's classic cab signal system is different. That is why international sets carry upto six different signaling system interfaces on them. They are each a veritable museum of signaling and train control system, on board segments. So it is a long stretch to claim that "all EU countries have PTC installed on their entire network". It is an even further stretch to claim that "all those systems are interoperable".
Also it is worth remembering that they operate under different regulations that in some cases are less stringent than FRA's.
Asia has very little PTC installed outside of new HSRs, and some dense suburban and subway systems, so I don't know what is there to look for there regarding PTC.
TVM430 and ERTMS are not interoperable in the normal sense of the term. Trains need to carry both equipment to operate on routes that require different systems on different segments. Or alternatively a route needs to be equipped with both, like LGV Est is.
Track-wise I think we should focus on upgrading incrementally. We need to stop trying to build high speed rail as a stand alone system. Most countries upgraded existing infrastructure and built the highspeed lines out in the rural areas and used the existing network to reach them. We should focus on reducing bottlenecks and raising average speed. Average speed is much more important than top speed, it doesn't matter if a train runs 150, 200, 220 for some portion of a route if it doesn't result in high average speed. Running 110 consistently is better than hitting 150 sporadically for short periods. Amtrak should aim for a 70-80 mph average and freight should go for a 60 mph average.
The freight part won't happen because on many many routes freight has max speed of 60mph, and on the fewer higher speed routes it is 70mph. There is no commercial incentive to raise speeds beyond that, since running at higher speeds requires more energy, the cost of which is going up considerably of late, and the difference in running time is inconsequential in terms of additional revenue opportunities as perceived by the railroads.
When one is dealing with existing rights of way, one cannot wish away its existing shape, which restricts speeds on considerable portions of them. Given that, what one needs to do is figure out an optimum speed profile to achieve best start to stop schedule times and go for achieving that, instead of working with preconceived notions like "running consistently at 110mph rather than 150mph sporadically", since consistent 110mph running may not be achievable in the track profile available. What Amtrak is trying to do on the NEC is an example of trying toget the shortest running time given the realities of the RoW profile and existing traffic conditions.