TWT,, the train moves in 3 dimensions, right.
But it is controlable in only 1 by the operator - forward and back - hence no steering wheel. The automobil is controlable in 2 dimensions - steering wheel is for left and right, the gearbox and pedals is forward and back.
The aeroplane is controlable in all 3 dimensions.
The dimensions correspond to line - plane - space
Nic