What does the bridge formula do when axles are placed close together?

Answer: B — It permits less maximum axle weight for axles that are close together

The bridge formula determines how much weight a group of two or more axles can carry based on how far apart those axles are as they cross a bridge. When axles are placed close together, the load is concentrated over a shorter distance, which increases the bending stress on the bridge. To protect the structure, the formula reduces the maximum allowable weight for that axle group. If axles are spaced farther apart, the load is spread over a longer section of the bridge, allowing more weight for the group. So, axles that are close together must follow a lower maximum axle weight. This rule applies to groups of two or more axles, not just steer axles.