How do they stay on the tracks?
By good engineering is the answer. The same answer as one will get if one asks : how do trains stay on the rail tracks?
When all is said and done, any wheel is levitating. Nothing touches anything. In the usual train tracks, the electromagnetic interactions of the wheel with the grooves surrounding it are what is keeping the wheel on the track. The grooves and wheels are engineered so that all the forces are compensated and the wheel keeps in the groove. The normal grooves are machined to line up the molecules of the metals in the proper geometric form to support safely a moving train and its weight. But nothing is "touching", there is always a "space" covered by electric/magnetic fields .
Levitating lines need different engineering, the magnetic fields have to be designed so as to compensate for the forces, downward and centrifugal, so that the train stays on track.