The 13 Controlling Criteria
The Green Book covers a wide range of geometric elements and design dimensions. In the interest of focusing the attention of the design profession on the most important or critical elements, FHWA performed a technical review of the adopted minimum criteria in the Green Book, with the understanding that requiring a design exception evaluation for every design element was impractical. Thirteen criteria, commonly referred to as the 13 controlling criteria, have been identified by FHWA as having substantial importance to the operational and safety performance of any highway such that special attention should be paid to them in design decisions. FHWA requires a formal written design exception if design criteria on the NHS are not met for any of these 13 criteria, listed below.
Stopping sight distance
Lateral offset to obstruction
States or other agencies may add additional design elements to this list, but the 13 controlling criteria reflect FHWA decision making and form the basis for formal written design exceptions on the NHS. See Chapter 3 for additional information.