System for determining the speed of a guided vehicle and/or the distance travelled by said guided vehicle, the latter being guided along a route by at least one rail, the system comprising: - a laser beam emitter configured for emitting a pulsed laser beam aligned with a first direction configured for pointing to a first location on a rail surface when the system is installed on-board the guided vehicle and the latter is guided by said rail along said route; - at least one IR detector (12, 13) configured for having a field of view (F21, F22) aligned with a second direction (D21, D22) in order to point to a second location on the rail surface when the system is installed on-board the guided vehicle and the latter is guided by said rail along said route, wherein the second location is separated from the first location by a predefined distance ΔX; - a processing unit configured for controlling the laser beam emitter according to control parameters and for determining the distance travelled by the guided vehicle and/or its speed from the predefined distance ΔX, a signal (SD1, SD2) related to a detection by the IR detector (12,13) of a warm spot at interaction area (I1, I2, I3) of the laser beam pulse with the rail surface and said control parameters of the laser beam emitter, the system being characterized in that it comprises a feedback loop designed for controlling a pulse frequency or a duration of the laser pulse of the laser beam emitter by means of the processing unit and for detecting a first pulse emitted by the laser beam emitter when the guided vehicle starts moving, wherein, for the detection of the first pulse, the processing unit is configured for controlling the laser beam emitter so that it either increases the duration of the laser pulse or increases the pulse frequency so that the resulting consecutive warm spots intersect with each other on the rail surface, until the IR detector (12, 13) detects a first warm spot. - a laser beam emitter configured for emitting a pulsed laser beam aligned with a first direction configured for pointing to a first location on a rail surface when the system is installed on-board the guided vehicle and the latter is guided by said rail along said route; - at least one IR detector (12, 13) configured for having a field of view (F21, F22) aligned with a second direction (D21, D22) in order to point to a second location on the rail surface when the system is installed on-board the guided vehicle and the latter is guided by said rail along said route, wherein the second location is separated from the first location by a predefined distance ΔX; - a processing unit configured for controlling the laser beam emitter according to control parameters and for determining the distance travelled by the guided vehicle and/or its speed from the predefined distance ΔX, a signal (SD1, SD2) related to a detection by the IR detector (12,13) of a warm spot at interaction area (I1, I2, I3) of the laser beam pulse with the rail surface and said control parameters of the laser beam emitter, the system being characterized in that it comprises a feedback loop designed for controlling a pulse frequency or a duration of the laser pulse of the laser beam emitter by means of the processing unit and for detecting a first pulse emitted by the laser beam emitter when the guided vehicle starts moving, wherein, for the detection of the first pulse, the processing unit is configured for controlling the laser beam emitter so that it either increases the duration of the laser pulse or increases the pulse frequency so that the resulting consecutive warm spots intersect with each other on the rail surface, until the IR detector (12, 13) detects a first warm spot.