The Indiana Department of Transportation (INDOT) began implementing volumetric acceptance of hot mix asphalt (HMA) mixtures in 2001. In some cases the air void contents of the plant-produced mixtures have been less than 2.0 %. Rather than require removal and replacement of low air void mixes in all cases, INDOT implemented an optional referee testing procedure. This procedure allows contractors to leave low air void material in place, at reduced pay, if the stiffness of the placed material is equal to or greater than a specified minimum. If the stiffness is less, that sublot must be removed and replaced. The rationale is that if the stiffness is high enough, even if the air voids are low, the material would be expected to perform adequately. If the low air voids are accompanied by low stiffness, rutting performance would likely be compromised. This paper describes the rationale, development, and implementation of this program.