ORIGINAL: ColinWright
Maybe there's something here I haven't considered, but...
I was mapping Eastern Anatolia, and getting mildly annoyed because, on the one hand, rivers cost movement points in OPART, but on the other hand, in reality, river valleys are usually the main avenues of movement -- even when there aren't roads.
Of course, generally, what costs movement isn't moving along the river, but crossing the river.
I don't see how moving along a river should be as cost free as moving along an open, flat plain. The river meanders, it has side tributaries, it cuts out gorges that may even need tunneling, etc. Think of the difficulty of putting in a road through a mountain gorge vs. through Kansas. The real reason the river is the avenue of movement in those cases isn't because it's so easy to move along the valley, but because it's so difficult or impossible to move by any other path. That needs to be effected by judicious use of alpine, escarpments, etc.
Wouldn't it work better overall if the movement penalty was charged for exiting the river hex rather than entering it? Pros, cons, and special cases of course, but it seems to me that this would still exact the cost for crossing the river without exacting a penalty for moving along it.
That, in and of itself, wouldn't accomplish anything. The cost of moving along the valley would be the same. Only if the game handled all the permutations of how the river hexes could be configured and associated together could what you want be effected. And that would be a huge task. It would even have to consider which side of the river the unit was moving on - the side with the branch or the side without.