The cost of the South Dakota portion of TransCanada Corp's Keystone XL pipeline has more than doubled to $1.974 billion in the last four years the project has awaited federal approval, the company said in a petition filed with the state Public Utilities Commission on Monday. The leap in costs from the previous 2010 estimate of $921.4 million is due to factors including the protracted regulatory process, inflation, currency changes, labour cost increases and materials storage, TransCanada spokesman Shawn Howard said.