Why do some small bridges have weight limits that depend on how many wheels or axles the crossing vehicle has?

The weight can be defined as the force exerted by gravity on an object. This gravitational force is known to be a vector quantity in some cases.

Varying cars carrying the same load but with different axle counts will exert different pressures on the bridge.

The contact area of the vehicle with the bridge rises as the number of axles increases, and the pressure produced by the vehicle is distributed along the contact area, causing less pressure on the bridge and causing less damage to the bridge.

The contact area of the vehicle with the bridge reduces as the number of axles increases, and the overall force exerted by the vehicle is concentrated over a smaller area. As a result, the pressure applied will be greater, causing greater damage to the bridge.

Smaller bridges, for example, have weight limits based on the number of wheels or axles on the vehicle traversing them.