Original: If the Chelseaâ "Hackney line were to be built it would relieve a lot of congestion on the Victoria line, offering an alternative route across Central London between Victoria and King's Cross St. Pancras.
Simplified: If the Chelseaâ "Hackney line is built then it will relieve a lot of congestion on the Victoria line. It will offer an alternative route across Central London between Victoria and King's Cross St. Pancras.