The possible mode of transport of the future is the amphibious, single wheeled, pedal powdered, submarine.
And below is a 3d model of it made in 123d design desktop, available to download here- http://www.123dapp.com/design .
Now if you want to know how i made read on ( and i recommend this) but if you just want the 3d model here it is - http://projects.123dapp.com/smb-123D_Design/monowheel-submarine/1783645 .
And don't forget to vote for the monowheel submarine in the 123d design contest if you think it should win.
Step 1: Starting off
Next draw a circle of any size, then draw another circle a little smaller than the first in the middle of it.
Now use the pull tool and pull the gap between the two circles outwards.
Then use the draw tool to draw 8 fins and pull them to the same height as rest of the model.
After that draw a square a little bit smaller than the inner circle in the center of the circle, this will be were the driver sits.
Next find the center of the square and draw a circle from the center of the square to the corner.
Finally pull the 4 outer parts of the circle you just made to the same height as the rest of the model.