While 94 percent of the bridges in the United States are built from concrete or steel, they aren’t your only choices. Timber, the earliest material for constructing bridges, and plastic, the newest material, are also viable options to consider.

Timber. Nearly 30,000 timber bridges are still in use today, and state and local agencies continue to build more. A timber bridge that is properly designed and constructed can carry the same load as a steel or concrete bridge. It has the advantages of being light weight, resistant to the effects of deicing agents, and can be constructed in any type of weather. However, wood preservatives must be properly applied to keep the wood from deteriorating.

In the 1990’s, the construction of new timber bridges got a boost from the USDA Forest Service’s National Wood in Transpor­tation Program. Under this program, local governments could receive up to 50 percent in matching funds for projects that advanced modern timber bridge design.

Plastic. The newest option for short-spans is plastic. Made from such materials as Recycled Plastic Lumber (RPL) and Fiber Reinforced Polymer (FRP), these bridges are seen as the future by many agencies. These bridges have many advantages. Weighing one-half to one-quarter of the weight of bridges built from traditional materials, they require less maintenance than steel, concrete, or wood. Plastic bridges can be installed very quickly, sometimes in a single day. The question remains as to how well plastic bridges will stand up to daily wear and tear. Also, the compatibility of FRP beams with various types of wearing surfaces is still being evaluated.

Many bridge projects that use FRP composites are funded through FHWA’s Innovative Bridge Research and Construction Program, which has given out grants to over 150 projects that advance the use of this new material.