There are two options available when defining the roadway profile: constant elevation and irregular. With the constant roadway elevation option selected, a prompt will ask to enter values for the crest length and elevation of the roadway, shown in the figure below. While not necessary for culvert hydraulic calculations, the beginning station of the roadway is also entered (the default is 0.0 and does not need to be changed if the station is not known or wishing to exclude the station). By defining the beginning station, culverts can be located laterally and displayed in proper relationship to the roadway in the front view. When the irregular profile shape is selected, a prompt will ask to enter between 3 and 15 points defining the station and elevation of each point along the roadway profile. A prompt will ask to enter a beginning station for the roadway when viewing the culvert from the front using the Views toolbar.
The length for a horizontal roadway is somewhat arbitrary but should reflect the top width of the water surface in the channel upstream from the culvert at the roadway elevation. Roadway width includes the shoulders, traffic lanes, and median.