The Tennessee Department of Transportation (TDOT) has approved the longitudinal installation of large diameter, corrugated high-density polyethylene (HDPE) pipe for storm water drainage systems. Approval came after its yearlong field test completed in June 2012 that showed no notable defects, deflection or stress on the pipe buried with shallow cover and fill height depth of 3 to 4 ft. Since 2007 the TDOT has allowed the pipe to be used for cross drains, transverse median drains and storm drain systems with up to 18 ft of fill height. Previously, longitudinal use was limited, for example, to side drains under driveways.