The idea is to make it worth while using the right train for the right job, rather than the fastest most powerful engine all the time.
It isn't necessarily final, i have tested it but not all engines or in all situations and i'm open to input if anyone else is interested in the idea.
I've converted the original set (relx2), train engines only and not yet done NG engines.
The formula has grown to be rather complex, but in a nutshell:
((first 50 mph)x0.
+((additional mph)x1.2) + ((first 500 HP)/50)+((additional HP)/20) -
(year/2)
This is then multiplied by a different number based on locomotive type to give a value for runcostfact, and a different number for costfact.
The discount rate for mph&HP is to help treat multi-headed units fairly, and the year value is included to provide a slight discount for newer engines with similiar stats.
As there are no low speed, high power or low speed, low power engines later in the game i'm considering either modifing 1 or 2 engines to better suit their purpose, or a 3rd tier set of carriages with modified speed later in the game. The engines would be a better option i think, and i'd appreciate advice on which engines to adjust, or new engines i can include.
Backup your existing files as i don't include the originals or an undo.
The mod:
http://www.pattinson.id.au/loco/