This final rule provides that operators may not transport a hazardous liquid in a steel interstate pipeline constructed before January 8, 1971, a steel interstate offshore gathering line constructed before August 1, 1977, or a steel intrastate pipeline constructed before October 21, 1985, unless the pipeline has been pressure tested hydrostatically according to current standards or operates at 80 percent or less of a qualified prior test or operating pressure. In addition, this final rule creates a comparable requirement for carbon dioxide pipelines constructed before July 12, 1991, except for production field distribution lines in rural areas. The purpose of this final rule is to ensure that the affected pipelines have an adequate safety margin between their maximum operating pressure and test pressure. This safety margin is essential to prevention of particular kinds of pipeline accidents.