Simulation of the road's International Roughness Index (IRI) for different tolerances in surface levels

The objective of this paper is to study effect of the acceptable tolerances in road surface levels on the obtained international roughness index iri. a factorial design with 78 design points was created to investigate the effect of variation in road levels on the obtained iri. for straight grades,the experimental factors were tolerance and percentage of points without any deviation in level. for vertical curves,the experimental factors were tolerance,percentage of points without any deviation in level,and the k value of the vertical curve. the study used a simulation approach to create road levels with stochastic variations within preset tolerances equal 1,2,and 3 mm. results showed that for tolerance of a 3-mm,at least 50% of the points should have no variation in levels in order to achieve an iri of about 1.75. to achieve an iri value equals 1.2,percentages of points without variations in levels should be 70% and 50% for tolerances 3 and 2 mm; and levels of the remaining points lay within the acceptable tolerance. for the 1-mm tolerance,iri of less than 1.1 is expected if all points satisfy the 1-mm tolerance.