"INTRODUCTION Drainage facilities@ like all other elements of the highway system@ deteriorate and decay due to the persistent forces of nature. Processes such as abrasion@ corrosion@ and erosion can lead to structural deficiencies and shorten the anticipated service life of drainage facilities@ eventually necessitating some type of repair or replacement. The purpose of this chapter is to discuss the various processes that can lead to culvert failure and the factors to be considered in selecting an appropriate repair or rehabilitative strategy. Any determination of appropriateness must consider many of the factors that led to the original design conclusions@ such as existing conditions@ projections of future needs@ material availability@ cost@ and environmental compatibility. In addition@ the designer has the opportunity to evaluate what has or has not worked at the locations in question and the ability to incorporate new technologies that may not have existed at the time of the original design. In addition@ this chapter will present information to help designers select culvert materials that have the greatest potential to attain the necessary design service life@ given a variety of site conditions and constraints. Many thousands of kilometers [miles] of roadways were constructed during the building boom of the 1950s and 1960s as part of the development of our system of interstate highways. To protect the vast investment in this system and the network of other State and local roads@ pavement management systems and bridge management systems have been developed and adopted. Although bridge management systems include those culverts with a span in excess of 6.1 m (20 ft)@ few entities have adopted similar systematic programs for the inspection@ evaluation@ and repair of drainage structures with spans below the 6.1-m (20-ft) ""bridge"" designation. Perhaps because culverts are less visible than bridges and pavement@ they have been given far less attention. However@ the aging of the interstate system and other routes@ combined with the lack of drainage system inspection and maintenance@ has resulted in hundreds of thousands of culverts that are nearing the end of their useful service life. This chapter will address these non-bridge sized culverts."