A ground-based power supply system for unguided electric vehicles, having a pair of supply tracks comprising a phase conductor track adapted to be set to a supply voltage, and a so-called neutral conductor track for current return, the phase track consisting of a plurality of segments (11.i) No. i, i = 1 to N, arranged end to end, each segment being electrically isolated from its neighbours, wherein the system comprises: a voltage source capable of supplying a supply voltage (V s); a switching block (30.i) associated with each segment and configured to selectively connect said segment to the voltage source and selectively disconnect said segment from the voltage source; at least one speed determination unit (500.i) capable of determining the speed of an unguided electric vehicle travelling on a roadway equipped with said power supply system; a set of first antennas each associated with one of said segments, such that each first antenna (520.i) extends along the segment (11.i) associated with it; a control device (50.i) comprising a control unit (502.i) capable of acquiring the speed of a vehicle determined by the speed determination unit, comparing the measured speed with at least one threshold speed (V 0) and controlling the switching unit as a function of at least the result of the comparison; said system being characterised in that it further comprises a set of second antennas each associated with one of said segments, distinct from the first antennas and such that each second antenna (521.i) extends along the segment (11.i) associated with it; each of the first and second antennas being adapted to pick up a signal emitted by a transmitter with which a skid of the vehicle is equipped, and to generate a signal representative of said picked-up signal; the speed determination unit being configured to determine a speed of the vehicle as a function of the signal generated by the first antenna associated with a first of the said segments and as a function of the signal generated by the second antenna associated with a second segment immediately adjacent to the said first segment and preceding it, in the direction of travel of the vehicles; said control unit (502.i) being adapted to control the switching unit (30.1) associated with said first segment to selectively connect said first segment to the voltage source, selectively disconnect said first segment from the voltage source as a function of the comparison of said speed thus determined with said threshold speed (V 0). a voltage source capable of supplying a supply voltage (V s); a switching block (30.i) associated with each segment and configured to selectively connect said segment to the voltage source and selectively disconnect said segment from the voltage source; at least one speed determination unit (500.i) capable of determining the speed of an unguided electric vehicle travelling on a roadway equipped with said power supply system; a set of first antennas each associated with one of said segments, such that each first antenna (520.i) extends along the segment (11.i) associated with it; a control device (50.i) comprising a control unit (502.i) capable of acquiring the speed of a vehicle determined by the speed determination unit, comparing the measured speed with at least one threshold speed (V 0) and controlling the switching unit as a function of at least the result of the comparison; said system being characterised in that it further comprises a set of second antennas each associated with one of said segments, distinct from the first antennas and such that each second antenna (521.i) extends along the segment (11.i) associated with it; each of the first and second antennas being adapted to pick up a signal emitted by a transmitter with which a skid of the vehicle is equipped, and to generate a signal representative of said picked-up signal; the speed determination unit being configured to determine a speed of the vehicle as a function of the signal generated by the first antenna associated with a first of the said segments and as a function of the signal generated by the second antenna associated with a second segment immediately adjacent to the said first segment and preceding it, in the direction of travel of the vehicles; said control unit (502.i) being adapted to control the switching unit (30.1) associated with said first segment to selectively connect said first segment to the voltage source, selectively disconnect said first segment from the voltage source as a function of the comparison of said speed thus determined with said threshold speed (V 0).