To clarify a few things:

> Remember the NTSB is a Government body with a mission. They are not concerned with Making a profit or if any of its recommendations meet any reasonable cost-benefit analysis. If they did, they would never have recommended PTC as it doesn’t meet any reasonable standard.

"Recommended" is the key word. That's all the NTSB can do in things railroad: recommend. They can't even show up to an accident of their own volition, someone has to call them. The FRA, the agency which has jurisdiction, has the authority to show up uninvited (and make binding "recommendations").

PTC was mandated by the FRA (and Congress) after Chatsworth. Someone who was on the inside of the Congressonal process told me that Congress had either or was about to adjourn without taking action on a new RR safety law when news of the wreck arrived. It reconvened and passed the new law by the end of the day. My source said that no one had seen Congress act so quickly.

By 2017, the FRA had recognized and certified 10 different PTC systems. Most of these have fallen by the wayside, with the US freight RR standard becoming I-ETMS and Amtrak on the NEC using ACSES II. Since the two systems aren't interoperable, freight locomotives which operate on the NEC must be equipped with ACSES II, and Amtrak locomotives which operate on the freight RRs must have I-ETMS. There's an Atk operation in Michigan which uses ITCS, but it's been very problematic. A number of transit-only operations have adopted forms of PTC, but these aren't under the purview of the FRA unless they operate on RRs which carry freight, like SDMTS and SMART.