Pavement performance models play a vital role in any pavement management system.
The Regional Government of Biscay (RGB) (Spain) manages a 1200 km road network and conducts
pavement data collections, including the International Roughness Index (IRI) values. The aim of the
paper is to develop an IRI performance model for two-lane roads with flexible pavement until the
first maintenance and/or rehabilitation activity is performed. Due to the huge amount of available
information, a deterministic model was selected. A literature review of deterministic models showed
that, apart from age and traffic volumes, the pavement structure is a key factor. Therefore, it was
decided to analyze the only road stretches whose entire pavement section was known (surface layer
+ base + subbase). Various variables related to age, traffic volumes and employed materials were
introduced as possible factors. The multiple linear regression model with the highest coefficient of
determination and all the variables significant included the real pavement age, the cumulated heavy
traffic and the total thickness of bituminous layers. As the material employed in the surface layer
could affect roughness progression, a qualitative variable was introduced to consider various surface
materials. The model improved its accuracy, indicating that the surface layer material is also an
influencing factor on IRI evolution.
