What is one of the main challenges of diagonal roadways across a slope?

Diagonal roadways across a slope lead to a larger disturbance of land primarily because they cut across the natural contours of the terrain. This alignment often requires more extensive grading and excavation than roads designed to follow the natural topography, which is typically perpendicular or parallel to the slope. As a result, constructing diagonal roadways can result in significant land alteration, leading to increased soil erosion and potential habitat disruption.

The other options, while potentially relevant in certain contexts, do not address the primary concern associated with diagonal roadways. For instance, while steep grades may be a concern, it's not universally applicable as it depends on the specific slope conditions. Similarly, maintenance requirements and traffic pattern disruptions could vary based on multiple factors not inherently linked to the diagonal orientation itself.