Culverts: Hidden Structures, Critical Infrastructure Elements

The U.S. transportation system is vast. Roadways and railroad beds cross small rivers, streams, and drainage channels millions of times, and each crossing requires a culvert to provide drainage without disrupting the flow of traffic. Numbering in the millions, culverts form a critical element of the national infrastructure. Guidelines for design and installation of culverts have evolved from manufacturers' trade associations to the current detailed American Association of State Highway and Transportation Officials (AASHTO) specifications, which control routine drainage culverts as well as small bridges with spans of 50 to 80 ft (15 to 24 m). AASHTO has developed these specifications through extensive federal, state, and industry research. Challenges exist in keeping the existing culvert population functioning and in improving the service life of new culverts. Key areas for improvement include improved asset management to monitor the culvert population, improved joint design and testing, and development of culvert inlet, outlet, and barrel rehabilitation materials and procedures. Vigilance must be maintained to see that good practice is used in construction of culvert installations. Through the use of improved materials, design practices, and construction procedures, more durable culvert installations can be achieved. This paper explores the growth of culvert design, construction, and material practices; assesses the existing condition of the culvert population; and identifies critical issues for keeping that population and our highways, healthy for the coming years.