The National Road Network (and many other datasets) are published with fields containing explicit domain description values, along with accompanying documentation that describes the domains of values for those fields. When designing a Geodatabase for these datasets, it's often the choice of the designer to create a Geodatabase coded value domain and apply it to the corresponding field(s) in the imported dataset. This script tool allows the Geodatabase designer to calculate domain code values for a field from domain description values in another field.

Download the Calculate Domain Code Field script tool from the ArcGIS Resource Center.