The railroad will be a interesting way to conect the user colonies.
It’s difficult to envisage a system within a relatively small-scale RTS like AoE in which laying railway tracks is a good idea. If it’s spammable (even if expensive) it will be abused, and it’s not the kind of infrastructure that I can see being viable in a game of this scale. It’s certainly possible that - like in AoE III - there will be existing railway tracks, but with maps of the size and type of an AoE game, actually laying tracks between point A and point B seems very odd – for a start, it logically has to benefit both parties.
The way AoE III used railways worked pretty well, because you had existing trade routes which were simply upgraded as newer techs became available. I can sort of see a system whereby railways are somehow automatically laid across trade routes, but manually laying track seems like something that would somehow be exploited.
But hey, I could be totally wrong, and I’m sure at some point within the next 2-3 years we’ll find out.