### While designing a large$-$scale transportation infrastructure project such as a highway or railway system, what are the key considerations that civil engineers must take into account to ensure the project's feasibility, safety, and sustainability? Discuss the theoretical frameworks and principles that guide the planning and design process, including aspects such as environmental impact assessments, geotechnical investigations, traffic flow analysis, and the integration of smart technologies. Additionally, elaborate on the role of regulatory standards and the importance of interdisciplinary collaboration among engineers, urban planners, and environmental scientists. How do these elements combine to create a cohesive and effective transportation network, and what are the potential challenges that engineers might face during the project lifecycle?