So we add a new item where, when you insert let’s say 64 coal, you have a fuel efficiency of 1. using a slider you can increase or decrease the efficiency, 2x efficiency means you go 2x slower but use 2x less fuel per whatever. that way we can get faster trains but also balance it a bit
example:
0.5 efficiency means you go 2 times faster but consume 2 times more fuel than normal
feel free to change the numbers as you see fit