The only one I can think of that MIGHT be compliant is UTA. When they built the commuter line out of Salt Lake a few years ago I recall hearing that they installed some early form of what sound to essentially be PTC. No intermediate signals, stories of repeated warnings and some penalty applications as you got close to the speed limit. Not sure if it has all the bells and whistles or is compatible with any other PTC system, but they might actually have something that is working on their smaller basically isolated system.

I heard someone suggesting part of the Northeast Corridor is equipped but I'm guessing an earlier system only on the high speed lines - and is it compatible with anything else?

Ironically it is the commuter lines that are suffering the most trying to get their act together. This unfunded mandate caught them off guard. Their funding, budget and granting cycles took several years, then they have play the drawn out contract game to find a design consultant, purchase not yet in production parts and then find someone to install it - plus rely an the Class 1's for all, part or some of their routes. Not to mention the railroads are scrambling to buy the frequency bandwidth in urban areas where they are apparently competing with cell phone companies. Seems Congress forgot to direct the ICC to give PTC priority and allocate enough bandwidth. I've even heard of problems installing needed towers on tribal lands.

And don't forget - they want digitally controlled electronic brakes next for "safety reasons"!