Abstract
Properly designed and constructed unbound aggregate layers have the potential to improve pavement performance and longevity. This study gathers information on the current state of practice and research on unbound aggregate. The study finds that no common practice exists among state transportation agencies. Accordingly, the report summarizes important aspects and effective practices related to material selection, design, and construction of unbound aggregate layers. Prevalent agency practices are summarized and key lessons learned from research studies are highlighted. Information for this study was acquired through a literature review and surveys of state and Canadian transportation agencies. (Author/publisher)