Seal coats or porous friction courses are allowed but not in combination. Fabric interlayers and Stress Absorbing Membrane Interlayers are permitted between the original surface and the overlay. Pavements which have been overlaid more than once since they were originally constructed are not studied. Sampling design factors for GPS-6A are moisture, temperature, subgrade type, traffic rate, original pavement structural number, overlay stiffness, and overlay thickness. Sampling design factors for GPS-6B are moisture, temperature, subgrade type, traffic rate, original pavement condition number, original pavement structural number, and overlay thickness.
All factors have two levels.
The table below shows how a section may evolve to obtain such a designation. The GPS-7 data includes sections which were a part of the original LTPP experimental design for rehabilitated pavements, as well as those which have been added in response to changes in practice. Slabs placed directly on untreated fine-grained subgrade are not included. Seal coats or porous friction courses are allowed but not in combination. Fabric interlayers and Stress Absorbing Membrane Interlayers are allowed when placed between the original concrete surface and the overlay.