Illustrate the comprehensive design process of a multi$-$span bridge in civil engineering, beginning from the conceptual design phase through to detailed design and construction planning. Include considerations for load calculations, material selection, environmental impact assessments, and safety standards compliance. Discuss the role of modern software tools in the design and analysis of bridge structures, and how advancements in technology have improved the accuracy and efficiency of this process. Address the challenges engineers may face in each stage of the design process and how they can be mitigated through effective project management and interdisciplinary collaboration.