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The method involves periodically recording a standard acceleration detected by an accelerometer. A fast Fourier transform of a recorded signal is calculated. A signal state change is triggered when a frequency component of a greater amplitude corresponds to a frequency included in a preset interval, and recorded during a step of training during which the traveler carries out an autonomous displacement, for a time length higher than a reference value corresponding to a nominal time of autonomous displacement of a traveler inside a vehicle e.g. bus. An independent claim is also included for a downloadable computer program comprising instructions for performing a method for characterization of a state of a traveler between a mobile state and an autonomous state.