Bedömd vägojämnhet på vägar med låga IRI-värden

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Sven Dahlstedt

The reported investigation is one part of a project concerning methods for measurement of the longitudinal roughness of roads and the necessary accuracy. In this study the main focus was on the subjective experience of roughness on roads with low IRI-values, i.e. fairly good roads. Using the available roughness data it was also studied how much a random error, added to the IRI-values, would influence the calculated correlations with the subjective estimates. The investigation was carried out as a magnitude estimation experiment, in which some 20 observers made their estimates while travelling as passengers first in a car, and later in a lorry.

The main results of the study were as follows:

- Subjective roughness seems to be a linear function of roughness according to IRI within the studied roughness range.

- The reliability of the observers, and the agreement between them, seems better in the car than in the lorry.

- For the very smooth sections (IRI almost =0) the roughness experienced in the lorry might have been caused by other vibration sources than the road surface.

- For some road sections with a "non-typical" spectral composition of the road roughness it was found that the correlation between IRI and subjective roughness decreased considerably.

- Some observers had even stronger correlations between their subjective ratings and road profile expressed in RMS units than between their estimates and IRI roughness.

- The simulations of random errors added to the IRI-values showed that, within the studied range and with the fairly large number of observations (45), random measurement errors up to at least ± 0,2 IRI-units can be considered insignificant.

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