Coherence of road roughness in left and right wheel-path

The coherence function between road roughness in left and right wheel-path is studied. Empirical coherence functions are computed from 20 measured roads, with a total length of 520 km. It is found that the coherence estimates are similar, despite the wide range of studied road types. A one-parametric model, which describes the coherence using an exponentially decreasing function, is compared to the common isotropic model. It is found that the parametric model gives more accurate approximations of the empirical coherence functions than the isotropic model. An extensive vehicle simulation study verifies that the isotropic model is not accurate enough.