Railroad system.

[Android]

1. Are mobs as fast as the coal train?
2. Where do you get the fuel for the subway system?

[stern23]

Just raise the track up off the ground five or six blocks. That should keep it out of reach of the mobs for the most part. Except for those rare sniper skeletons. Those guys get on my nerves.

[yottabyte]

Hah, you plan using powered minecarts? That won't get you far. Please read some about Minecart Mania, it helps a lot. http://www.minecraftwiki.net/wiki/Minecart_Mania!

What I meant with mobs it that when you crash into an animal or a monster, the minecart stops. Stern's solution fixes that though.

[Android]

Ah ok, wasn't aware of the minecart mania thing. that makes things easier to understand.