To reduce both the initial and the maintenance painting costs, engineers in many states have increasingly been designing bridges made of bare, exposed weathering steel. However, after many years of experience, engineers are concerned about the long-term performance of weathering steel bridges. Nevertheless, as with all new materials, much research has been conducted to find solutions for atmospheric corrosion to enhance the successful application of weathering steel to bridges for more economic and environmental benefits

Numerous representative data show the corrosion behavior not only of weathering steel, but also copper steel, and carbon steel under localized microenvironment conditions investigated by many researchers: angle of exposure, orientation, shelter, continuously moist conditions, industrial pollutants, deicing salts, galvanic corrosion, pitting and crevices.  

The results and discussions demonstrate that uncoated weathering steels should not be exposed in the following conditions: marine or heavily industrial environment, high rainfall or humidity conditions, sheltered conditions, and some other bad design conditions. Therefore, for proper bridge design, the micro-environment as well as the macro-environment should be considered with caution and a study of previous experience by a corrosion engineer as a significant factor in preventing further corrosion.