A ground level power supply system includes a live track capable of being brought to a supply voltage and a neutral track for the return current, with the live track being constituted of rectangular segments; a first voltage source capable of supplying a low supply voltage and a second voltage source capable of supplying a high supply voltage, each segment being connected by a controlled selector either to the first voltage source, or to the second voltage source; a speedometer capable of measuring the speed of a vehicle travelling over a section of a roadway equipped with the system; and a selection device capable of acquiring the vehicle speed measured by the speedometer, then comparing the speed measured with a threshold speed, and controlling the selector based on the results of the comparison.