Effects of Design and Site Factors on Roughness Development in Flexible Pavements

This paper presents the relative influence of design and site factors on roughness development of in-service flexible pavements. The data from the specific pavement study (SPS)-1 experiment of the long-term pavement performance program were used to investigate the effects of asphalt concrete surface layer thickness, base type, base thickness, and drainage on roughness growth of flexible pavements constructed in different site conditions (subgrade type and climate). Since this is the first comprehensive study involving the SPS-1 experiment, a thorough data analysis methodology was adopted. The result of the analyses shows that among the design factors, base type was found to have the most significant effect on roughness progression. The pavement sections with asphalt-treated bases showed the best performance. Drainage and base type, when combined, also played an important role in inhibiting roughness, while base thickness has only secondary effects. In addition, climatic conditions were found to have considerable influence. Pavement sections in the wet-freeze zone exhibited a higher roughness increase. In general, pavements built on fine-grained soils have shown the worst roughness levels over time. Important interactions between design and site factors were identified; these should provide new insights in enhancing long-term flexible pavement performance.