The best design for a pasta bridge is using multiple triangles for stability. Spaghetti has strong axial tension but weak compression, so it is best to make compression lengths as short as possible and add internal web members.
According to PghBridges.com, two of the main factors in bridge-building are span and form. A span is the length of the bridge from end to end. A spaghetti bridge is either simple or continuous to account for the pasta's brittle nature. The travel surface of the pasta bridge is often in the deck configuration, meaning the chain of triangles is below the travel surface. Successful designs have also been through configuration, meaning the traffic travels through a truss made of multiple triangles that includes a cross-brace above and below. The truss is made of many smaller strands of spaghetti. The king post is the simplest design, consisting of two right-angle triangles connected at the short side. For a longer span, multiple king post trusses add length without sacrificing stability.
A pasta bridge is usually constructed using spaghetti and hot glue. When in a contest, typically the bridge is tested for strength halfway across with a dowel across the travel surface. The dowel holds a bucket into which weight is added. The bridge connections should be strong but flexible due to spaghetti's brittleness. When gluing the bridge, it is best to use just enough at the ends to hold them together. Otherwise the pasta cooks and becomes weaker.