4148.01GENERAL REQUIREMENTS
Meet the requirements of AASHTO M 178, standard quality, extra quality, or special quality, as specified, or AASHTO M 179, standard, extra quality, or heavy duty, as specified. When the quality is not specified, use extra quality tile in roadway embankments, and use standard or standard quality tile in other locations.
Source: Iowa Standard Specifications for Highway and Bridge Construction, 2023 Edition. Pages 1118–1118 of 1,288.