Arch bridges resist compression extremely well, while suspension bridges provide the best tensile strength. Since compression and tension are opposite in nature, it is not possible to guarantee that one type of bridge is the strongest against both.
The strength of a bridge can only be determined by its resistance to a combination of forces: compression and tension. Compression is the force that pulls both ends of a bridge together, while tension is the force that stretches them apart. When compression overcomes a bridge's resistance to its force, buckling occurs and the bridge fails. When tension pulls both ends of the bridge apart, the bridge snaps in half. Large bridges also suffer from shearing and resonance problems as a result of strong winds or currents.
Civil engineers design bridges to perform under the specific conditions of the environment they are being constructed in. For example, a suspension bridge performs well when pulled apart by heavy weight on each side, but can be destroyed by heavy winds.
The material used to build a bridge is another important factor to determining the strength of its design. Concrete is an excellent material for an arch bridge, due to its ability to withstand compression, but makes a poor choice for a suspension bridge.