Explore the theoretical foundations of transportation engineering, analyzing the principles governing traffic flow, capacity, and operational efficiency in transportation networks. Examine theoretical models of traffic behavior, including traffic flow theory, queuing theory, and network equilibrium models, to understand the complex interactions between transportation demand, supply, and system performance. Discuss the role of advanced technologies, such as intelligent transportation systems and traffic simulation tools, in optimizing transportation infrastructure planning, management, and operations. How do engineers leverage theoretical insights from transportation engineering to address contemporary challenges such as congestion, sustainability, and multimodal mobility in urban environments?