It is a bad idea to change any parameters except:
*Enable 4th rail - (Disabled by default because I don't know of a working 4th rail train newGRF)
*Introduce 4th rail with 3rd rail - (4th rail will only exist if you either have this setting on and there is a 3rd rail train or there is a 4th rail train)
*Enable 4th rail with catenary - (You should turn this on if you enable 4th rail)

You CAN use "Enable rails from year 0" BUT it might not be a fun to play. ;-)

You need to load this after PURR or BAD THINGS will happen.

Thanks to NuTracks for the graphics and for some code.

If you want to contact me email: skyem@hotmail.co.uk
(I don't check it very often though)