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
Northern Lights (pipeline) by the Vukhtyl gas field, but later the pipeline was extended in order to connect with the Urengoy gas field. The Northern Lights pipeline system has a total length of , of which around is used to transport Russian gas to Europe. The pipeline runs from the Urengoy gas field through Vuktyl, Ukhta, Gryazovets, Torzhok and Smolensk to Minsk in Belarus and from there to Poland, Ukraine and Lithuania. A part of the newer Yamal–Europe pipeline runs parallel to the Northern Lights pipeline. A branch line from Gryazovets through Saint Petersburg to Vyborg supplies the Saint Petersburg area and Finland.