In a sense: yes. Heavy, large, and all its mass is near its rim. For a flywheel, it's not _that_ fast, though; only about 125 revolutions/hour.

They got rid of the forces acting on the center of a flywheel that tear apart large fast flywheels by getting rid of the axle and using a rail on the outside of the wheel to counteract the centrifugal forces.

I would guess they want to use maglev as a rail system, as a conventional track may break down too soon at 2000 km/h. On the other hand, it is 'only' 15 km of rails in a controlled environment, and they can use enormous wheels, so it may be possible to lay conventional track a lot smoother than outside.