dirt road dusty

how do I make a dirt road dusty

Are you meaning dust on the ground or dust clouds, because dust on the ground can be achieved by having a material with high diffuse roughness, low specurity (or glossiness if you’re using Cycles), and a fine-grained bumpmap of low to medium intensity.

For dust clouds, you could possibly do it in BI by using a volumetric material that uses point-density texture and high contrast procedural specks. For Cycles, it can be faked via a speck texture combined with particle billboards that make use of a circular gradient to make the face edges transparent.