Summary: Caltrans has developed a modified binder (MB) specification for asphalt rubber binders. The initial specification was developed through a laboratory and field pavement performance study which included an evaluation of six field projects initially and reportedly validated on a number of additional field projects. Questions raised by industry regarding this specification include the following: (1) does the cup and plate test used by Caltrans quantify the asphalt rubber binder (2) is the cup and plate test repeatable within and between laboratories? (3) Are the failure criteria developed appropriate for asphalt rubber? (4) Were the lab and field data used to develop the failure criteria sufficient and has the failure criteria been adequately validated? (5) Were factors such as pavement geometry, mix design, existing pavement condition, materials, and construction practices considered in the development of the specification?