What is the purpose of bridge formulas?

Answer: C — Permit less maximum axle weight for axles that are close together

The purpose of bridge formulas is to determine the maximum allowable weight that can be legally placed on axles based on their spacing. The correct answer indicates that bridge formulas permit less maximum axle weight for axles that are close together. This principle is designed to prevent excessive stress on bridges and roadways. When axles are spaced closely, they can create more localized stress on the bridge structures. Therefore, bridge formulas account for this by limiting the weight distributed over such axles to protect infrastructure integrity. By enforcing these weight limits, bridge formulas help ensure that vehicles do not pose an undue risk to public safety and the longevity of road systems. In contrast, the other options do not accurately reflect the function of bridge formulas. They do not allow the same maximum axle weight regardless of spacing, as closer axles are indeed subject to stricter limits. Additionally, while the formulas can technically limit maximum weight based on spacing, they do not eliminate the need for weighing vehicles; such measurements are still essential to ensure compliance with legal weight restrictions.