system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't freight trains use turbine engines?

Freight trains in the US use diesel-electric drive trains where the engines act as a generator that then drives electric motors. These trains are supposedly extremely efficient, with a commonly-cited figure of 400 mpg per ton.

However, I'm operating under the assumption that turbines are the most efficient way to produce electricity as they're used to produce electricity for the grid. If this is the case, then why aren't trains using turbines, since they're trying to turn fossil fuel into electricity at peak efficiency? If it's not, then why do power plants not use diesel?
gpt
Because trains do a lot of idling as well. Turbines are ungodly inefficient at low speed (power)

There are several examples of turbine locomotives though. The opitomy of which were Union Pacific's General Electric turbine locomotives (GTEl's). Flooring 8500hp (and by some accounts capable of up to 10k.)

The main disadvantages comes in their size, and the massive amount of fuel.

The GTELs used a 3 unit consist for each motive into. By today's standards it would be underpowered (8500 vs 13k in flagship locomotives), they also used more fuel. The reason that UP's GTELs were economic for the time was that bunker C fuel had no other use (This was a time before advanced refining techniques) and it was first cheap.

They are/were also exceptionally loud.