Explain the theoretical framework and key factors involved in the design and construction of transportation infrastructure for urban environments. Start with an analysis of the principles of transportation engineering, including traffic flow theory, capacity analysis, and mode choice considerations. Then delve into the complexities of urban transportation planning, addressing topics such as multimodal integration, land use$-$transportation interaction, and sustainable mobility solutions. Discuss how factors like population density, land development patterns, and socioeconomic dynamics influence transportation infrastructure design decisions. Furthermore, explore theoretical approaches to optimizing urban transportation networks for efficiency, safety, and environmental impact reduction, considering emerging technologies and future urbanization trends.