Why do bridge engineers try to reduce dead load on long-span bridges?

In bridge engineering, the dead load refers to the permanent weight of the bridge structure itself, while the live load represents the traffic it carries.12

Engineers prioritize reducing the dead load on long-span bridges because, unlike short spans where traffic weight dominates, the dead load becomes the primary force acting on the structure as the span length increases. Because the bridge must support its own massive weight before it can even accommodate traffic, minimizing this weight is essential to structural efficiency.1

By utilizing advanced materials and structural forms—such as cantilever, cable-stay, or suspension designs—engineers can achieve greater strength using less material. Techniques like prestressed concrete further assist in this goal by allowing for lighter designs that counteract downward forces, ultimately making the construction more feasible and cost-effective.13