How do transportation engineering principles influence the design and operation of urban transportation systems, including roads, highways, and public transportation? Discuss the concepts of traffic flow theory, including traffic volume, density, and speed, in optimizing roadway capacity and reducing congestion. How do factors like land use planning, traffic demand management, and intelligent transportation systems contribute to the efficiency and safety of urban transportation networks? Furthermore, elaborate on the importance of sustainable transportation practices, including public transit, cycling infrastructure, and pedestrian$-$friendly design, in reducing carbon emissions and promoting sustainable urban development.