The longitudinal road profile is described by means of the power spectral density (PSD) and specified by two of its parameters, the unevenness index and waviness. This model with the waviness value equal to two is considered as the "standard" model. Besides this statistically based model, two semi-empirical indicators of longitudinal road unevenness (roughness) are used: the International Roughness Index (IRI) and the wave-band triad consisting of three variances in three adjacent wavelength bands: short, medium, and long. In the first part of the paper, mutual conversion relations between the standard PSD and the other two indicators are given. The main emphasis of the paper is on considering gradual departures from the standard model. Firstly, general forms of waviness values different in partial wavelength bands are taken into account. Further attention is paid to the presence of periodic components in the longitudinal profile. Some other types of non-standard forms of longitudinal road profile are also briefly mentioned.
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Kropáč et al. (2004) studied this question.
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