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
- 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
- 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.
Linköping: Statens väg- och transportforskningsinstitut., VTI rapport 474 , 2002.
Swedish, Sweden, Surfacing, Evenness, Comfort, Measurement, Driver, Attitude, Test, In situ, Car, Lorry