Optimal Design for Highway Drainage Culverts

Economic risks are directly considered in an optimal design procedure for box culverts. Flood related losses are computed on a probabilistic basis to derive economic risks for box culvert design. The components of economic risk are damage to upstream property, damage to the embankment and roadway, and damage to the culvert. An optimal design is reached when the construction costs plus the economic risks are minimum. The design procedure is applied to 22 case sites on rural interstate highway stream crossings in Virginia. Based on this economic risk procedure, curves are developed which suggest variable return period criteria for conventional design practice. The analysis focuses upon engineering and economic factors. A complete consideration of the design problem, in this day and age, also requires a professional sensitivity to environmental issues. For the conventional situations, construction cost savings on the order of 50% are indicated for the reinforced concrete barrels of the optimal design.