From my experience, the best materials depend largely on the specific use case of the bridge. For example, steel is great for long spans due to its high tensile strength, while concrete is more suitable for shorter spans with heavy loads.
Environmental impact is crucial. Consideration for local wildlife and minimizing disruption should always be a priority. In some cases, building with sustainable materials can also offer long-term cost benefits.
Load calculations are essential. Overestimating can lead to unnecessary costs, while underestimating can be catastrophic. Investing in good engineering software can make a significant difference.
Aesthetic design is often overlooked but is important for community acceptance and sometimes funding. Incorporate local cultural elements if possible to win over public sentiment.