TransCanada has obtained final approval from state officials in Nebraska to build the controversial Keystone pipeline across Nebraska, even though these same officials vetoed what TransCanada has viewed as the preferred route.

And while the final approval should mean that construction can begin, the realities are more complex, and even TransCanada itself says it will now have to review a number of factors relating to the pipeline's economic and political feasibility.

The Nebraska decision comes on the heels of the pipeline spilling 210,000 gallons of heavy tar sands crude in northeastern South Dakota. Officials at the South Dakota Department of Environment and Natural Resources don't believe the leak affected any nearby water bodies or drinking water systems. They also said that responsibility for the clean - up rests with TransCanada, and that the company had dispatched crews to clean the spill up within 15 minutes of the accident. The clean-up will likely continue for several months.

The pipeline transports crude from Alberta, Canada, to refineries in Illinois and Oklahoma, passing through the eastern Dakotas, Nebraska, Kansas and Missouri. It can handle nearly 600,000 barrels, or about 23m gallons, daily. TransCanada says on its website that the company has safely transported more than 1.5bn barrels of oil, or about 63bn gallons (with the exception of the South Dakota spill as well as several other minor spills), through the system since operations began in 2010.