1.1 This specification covers the requirements for smooth-wall perforated and nonperforated poly(vinyl chloride) (PVC) plastic pipe and couplings for use in subsurface drainage systems of highways, airports, and similar applications in nominal sizes of 4, 6, and 8 in. and in pipe stiffnesses (PS) that are designated as Type PS 28 and Type PS 46 in accordance with its minimum pipe stiffness. 1.2 Molded fittings for use with highway underdrain pipe are in accordance with Specification