Abstract: The invention concerns a method for estimating an International Roughness Index (IRI) of a road or road segment. comprising a preliminary step (1) and an International Roughness Index estimation step (10). The preliminary step (1) comprises collecting (2) values of vehicle tire damping and stiffness coefficients (Ct, Kt) and collecting (3) vehicle vertical acceleration values (Azvehicle) measured on vehicles driven at a constant speed along road segments to which known international roughness index values or known road profiles (profiler) are associated, as well as vehicle geo-referencing data and speed data indicative of the given constant speed associated with the measured vertical acceleration values (Azvehicle).