1) PIARC : Technical committee report on surface characteristics, 1978.
2) ASTM : Standard guide for classification of automated pavement condition survey equipment, Standard No.E1656-94.
3) ASTM : Standard guide for conducting subjective pavment ride quality ratings, Standard No.E1927-98.
4) Sayers, M.W. and Gillespie, T.D. : The international road roughness experiment, A basis for establising a standard scale for road roughness measurements, Transportation Research Record, No.1084, pp.76-85, TRB, 1986.