In Trainz (especially for steam locomotives or older diesel-electric locomotives), refers to the reverser (also called the cutoff or direction control), not the throttle.
Here is text covering the mechanics, usage, and simulation context of operating a train with half engine power versus full engine power.
When the throttle is advanced to Notch 8 (Full Engine), the locomotive is operating at maximum capability.
The Half Engine is a fictional locomotive that has become a staple of the Trainz community. It's a unique and highly customizable engine that allows players to create a wide range of scenarios and routes. The Half Engine is known for its versatility, power, and distinctive appearance, making it a favorite among Trainz enthusiasts.