This device will infinitely create track for your minecart, so it never ends!

Keep in mind: You need a redstone clock to power the commandblock, and the other 4 commandblocks in that world are that clock. It only works traveling North (For the world download)

To use in your world, use one of these commands
North
/execute @e[type=MinecartRideable] ~ ~ ~ execute @e[type=Player,r=0] ~ ~ ~ clone ~ ~2 ~ ~ ~ ~ ~ ~ ~-1
South
/execute @e[type=MinecartRideable] ~ ~ ~ execute @e[type=Player,r=0] ~ ~ ~ clone ~ ~2 ~ ~ ~ ~ ~ ~ ~1
West
/execute @e[type=MinecartRideable] ~ ~ ~ execute @e[type=Player,r=0] ~ ~ ~ clone ~ ~2 ~ ~ ~ ~ ~-1 ~ ~
East
/execute @e[type=MinecartRideable] ~ ~ ~ execute @e[type=Player,r=0] ~ ~ ~ clone ~ ~2 ~ ~ ~ ~ ~1 ~ ~

Then all you have to do is, place a redstone block with a powered rail on top, place a minecart, hop in, and start moving!
Remember that this will NOT change elevation and will tunnel straight through any mountain or building, and go above any chasms or holes.

Please remember to diamond, and at least click the download link, when you get to medaifire, you don't really have to download it, but at least click the link here, it helps.