OK, my solution to the Railroad dilemma involves a few fairly minor changes-well, OK, mostly minor with one fairly MAJOR change.
1) Keep unlimited movement for RR's, but ONLY if the RR hex is entered from a city, airport, colony, outpost, or fort. Otherwise, the RR counts as an 'advanced road', perhaps granting a movement bonus of 1/4 or 1/5.
2) If you leave a RR square outside of a city, then you lose ALL of your remaining MP's. If you pass from a RR, to a city, and back to a RR, then you lose 1MP. i.e. Your unit loses 1mp for every city it passes through along a rail line. Alternatively, you could have it that only a maximum no. of units, using rail, can 'pass through' a city in a given turn-to represent logjams at rail terminii. To make things more interesting, certain units can count as 'multiple' units for the purposes of this. So an infantry unit would count as ONE unit, a cavalry unit might count as TWO units, and tanks/modern armour count as THREE units. This would reflect the fact that it is easier to move large numbers of foot soldiers than it is to move lots of tanks and artillery!
3) Break everyones turn up into a movement phase and an attack phase. This will allow defenders to retaliate to an invasion by bringing forces up from the 'interior'-but only if they are within range.
4) Give RR's an ongoing maintainance cost-perhaps 1gpt/3-4 hexes. Roads would also have a cost, but would be more like 1gpt/6-8 hexes! This will help prevent players, and the AI, from simply railroading EVERY hex in sight, and perhaps force them to focus more on connecting up cities and connecting major cities to strategically important landmarks and terrain improvements!
What is important to remember here is that we are not simply focussing on 'Realism' in this instance, but also dealing with gameplay and aesthetic concerns. I definitely feel that my ideas, IMHO, would help deal with these concerns
Yours,
Aussie_Lurker.