A rail having an upper supporting edge and a lower braking edge, and a traction unit for riding on the rail and adapted to be connected to a carrier so as to suspend the carrier from the rail. This traction unit has a power-driven wheel to ride on the rail upper edge, and a plurality of braking wheels positioned close enough to the lower edge of the rail to prevent the traction wheel from jumping off the upper edge thereof, and a brake system for each brake wheel. A substantially C-shaped arm is pivotally connected to the traction unit near the top thereof and extends downwardly and around the rail and has a lower end extending across the plane of the rail, to which the carrier is connected.