UP's Big Boy got some upgrades after a year or two of touring the UP system. It no longer needs a Diesel helper. Previously, the helper engine carried the modern Positive Train Control gear, and the steam engine cab had a display connected by a cable to the Diesel helper. Now, UP 4014 has its own PTC gear and antenna in the tender, so it's self-sufficient. UP runs that engine on heavily used main line track, so it needs to be fully connected to safety and dispatching systems.

This was mostly a power problem. UP 4014 had a small steam turbogenerator atop the boiler to power lights and such. Now it has three such generators, and there's enough electric power to run auxiliary equipment.

UP did a serious rebuild on the Big Boy, to original main-line standards. Many parts were fabricated from scratch. It's ready for regular use for decades. Most heritage railroads lack the resources for such major overhauls.

Here's the first test run with no Diesel, in May 2024.[1]

[1] https://www.youtube.com/watch?v=khJZ6NO5rhQ

Oh, "PTC gear" as in equipment, not just one magical gear that prevents accidents, as popped into my mind at first!

Is PTC the first step in getting rid of human engineers, billed as a safety system?