There are more factors from bond vehicle – road condition that have significant impact on driving comfort on the road. One of indicators in this bond is roughness of roadway surface (smoothness), and with this indicator safe and comfortable driving at designed speed on particular roadway is ensured.

One of the most important surface parameters of every roadway is longitudinal roughness which is functionally connected with maximum allowed driving speed. Longitudinal roughness, expressed through International Roughness Index (IRI) is significant parameter which have to be achieved on pavement surface.

The occurrence of excessive plastic deformation, fatigue and the appearance of cracks in the pavement structure are factors that require on-going quest for a technical solution in order to obtain high quality flexible road construction especially for highways and roads with very heavy traffic load. Applying a design solution by overlaying or one-layer upgrading of pavement structure, is usually limiting factor in achieving of the required roughness.