This paper summarizes the results of a research project that investigated the use of thermoplastic pipes, namely High-Density Polyethylene (HDPE) and Poly-vinyl Chloride (PVC), as cross-drains under highways. The study evaluated pipes ranging from 0.3 m (12 in.) to 1.5 m (60 in.) in diameter, under deep fills, minimum cover, and construction loads. The project consisted of three major phases: (1) a comprehensive literature review, (2) an analytical study into the allowable fill heights for thermoplastic pipes, and (3) a field study to observe the installation and performance of the pipe in service conditions. This study concluded with recommendations for how and when thermoplastic pipe should be installed in order for it to perform as intended.