The first step in analysis for a cross-drainage facilityis the establishment of the flood frequency curve and the stage-discharge curve according to Chapter 4, , and Chapter 6, ; and the second step is to make a decision concerning the type of cross-drainage structure. All types of facilities should be appraised based on performance and economics. The choice is usually between a bridge and culvert. If the stream crossing is wide with multiple concentrations of flow, a multiple opening facility may be in order.

At many locations, either a bridge or a culvert will fulfill both the structural and hydraulic requirements for the stream crossing. The roadway designer should choose the appropriate structure based on the following criteria:

Although the cost of an individual bridge is usually relatively small, the total cost of bridge construction constitutes a substantial share of the total cost of highway construction. Similarly, bridge maintenance may account for a large share of the total cost of maintaining highway hydraulic features. The roadway designer can achieve improved traffic service and reduced cost by judicious choice of design criteria and careful attention to the hydraulic design of each bridge.