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, November 2008, 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 from the conference, and includes contributions on a variety of topics: Highway Design and Transportation Planning;Transportation Network and Management System Traffic Characteristics and Analysis Traffic and Transit Signal Control;Traffic Simulation, Safety, and Management;Advances in Road Safety EngineeringRoad Accident Analysis and Prediction;Work Zone Lane Closures and Dynamic Merging Flexible Pavement Design, Analysis, and Evaluation;Pavement Maintenance and Management;Binder and Emulsion Characterization;- Effect of Binder, Modified Binder, and Fillers on HMA HMA Testing and Properties;Foamed and HMA Recycling;Impact of Geogrids on Pavement Performance;Research, Development, and Standardizations Case Studies