That's not modified at all in GEM or civup. It's a vanilla issue I think from looking at the vanilla xml.
The cost of movement on roads decreases with a tech, at which point railroads are essentially the same for many units, and that's always been the case for Civ5 so far as I know. "Slower" units that move 2 might move slightly faster on railroads than roads but anything else is the same.
The utility of rails is the extra production, not a speed advantage as in previous civ games (it is sometimes claimed that it will though, which is a serious problem with the design. I think the intention was that they should decrease movement to 1/10 but they don't actually do that in the code, they decrease it to 1/3, like advanced roads). We could modify this easily enough (to 1/10 or 1/5 instead of 1/3?).
An alternative is to increase unit speed later in the game (as happens with WW2 era and on units in GEM).
