Approval from the federal government was necessary to begin construction, but the Santos' administration refused to authorize it. The subway plans contracted by Petro's administration were discarded by his successor Enrique Peñalosa, who opted for an elevated railway system with allegedly lower investment required and better coverage. These claims have been refuted by several independent studies that have found that both the social and economic cost of an elevated railway system is higher than the original underground railway system planned by the previous administration.[citation needed]