Internationally, significant attention is given to transport sustainability, including planning, design, construction, evaluation, safety, and durability of the road system. The 4th International Gulf Conference on Roads: Efficient Transportation and Pavement Systems - Characterization, Mechanisms, Simulation, and Modeling, hosted by the University of Qatar, provided a forum for discussions of recent developments and research results and needs on transportation network optimization, traffic management, transportation safety, and pavement design, analysis, material characterization, modeling, and rehabilitation techniques. This book is a collection of 79 fully refereed papers and six keynote lectures.