Disclosed is a rolling unit for a test rig for testing an automatic underground train, including: two rolling belts, each one provided for a wheel of the train to roll thereon, the wheels driving the movement of the belts; and a rotary inertial body; each belt including: a pinion that is rotatably connected to the inertial body; two rollers; and a grooved rolling surface mounted on the rollers, meshed with the pinion, and forming a rolling area for a respective wheel between the rollers.