ROAD SURFACE CONDITION DETERMINATION METHOD AND ROAD SURFACE CONDITION DETERMINATION APPARATUS

A method of determining a road surface condition includes: acquiring, when determining a condition of a road surface being in contact with a tire from a time-varying waveform of vibration of the running tire, the time-varying waveform of vibration having been detected by a vibration detecting means, a plurality of intrinsic vibration modes, from data of the time-varying waveform of vibration of the tire, using an algorithm of empirical mode decomposition; selecting an arbitrary intrinsic vibration mode from the plurality of intrinsic vibration modes; calculating a statistic amount from the distribution of feature data calculated by performing Hilbert transform on the selected intrinsic vibration mode to set the statistic amount as a feature amount; and determining the road surface condition from the feature amount and a feature amount obtained in advance for each road surface condition.