Truss spacing in this style of construction is typically between 2 and 4 feet, however sophisticated designs may allow for spacing of up to 8 or 12 feet. The longest truss bridge in North America is also based on this design: the Cherry Street Bridge over the Ohio River in Cincinnati. The depth of a truss bridge varies depending on its design but most are about as deep as their largest beam. The deck is usually made from steel plates fastened to the top of the pillars with girders running between them. The space below the deck is filled with more beams until it reaches the ground. Truss bridges are very strong because every part of the structure is used to support some of the weight above it. There are several types of truss bridges, each with its own characteristic layout of vertical and horizontal members. The most common type is the Pratt through truss, so called because the main diagonal members (known as "pratties") cross at right angles, like the legs of a "Z" shape. Other types include the Warren truss and the Bailey truss. On many older bridges, you will still find an illustration of how a horse's head was used as a prototype for the first trusses. These drawings are still used by some architects today when designing new bridges.