Construction of the Trans-Alaska Pipeline System for a fifth, should it become necessary. Holding tanks were planned that had a capacity equal to that of the pipeline, allowing the whole pipeline to be emptied if required. As required by the Pipeline Authorization Act, a ballast-water filtration system had to be designed as well. This system removes oil from tankers' ballast water so it is not released into Prince William Sound—something fishermen feared when the pipeline was proposed. Shortly after the permit was signed, convoys of equipment on snow tractors began heading north, using hardened snow roads and an ice bridge over the Yukon River to reach
Pipeline transport remotely, from what is usually known as the "Main Control Room". In this center, all the data related to field measurement is consolidated in one central database. The data is received from multiple RTUs along the pipeline. It is common to find RTUs installed at every station along the pipeline. The SCADA system at the Main Control Room receives all the field data and presents it to the pipeline operator through a set of screens or Human Machine Interface, showing the operational conditions of the pipeline. The operator can monitor the hydraulic conditions of the line, as well as send