You just can’t get tar sands (bitumen) sludge through pipelines. Most train terminals are hundreds of miles away from the extraction fields. How get the sludge there? Mix in some “diluent” so the sludge can move through the pipelines. The combination of diluent (28%) and bitumen (72%) creates a thick black cocktail the oil industry calls “dilbit“.
The problem? Dilbit has a much lower flash point than raw tar sands. In fact, it has an ignition point at -35ºC, compared to -9ºC for conventional light oil.
As per RailwayAge website: “The widespread belief that bitumen from Alberta’s northern oil sands is far safer to transport by rail than Bakken crude is, for all intents and purposes, dead wrong.”
Here are 2 articles that lay it all out:
From RailwayAge (written by David Thomas): http://www.railwayage.com/index.php/safety/why-bitumen-isnt-necessarily-safer-than-bakken.html
From Oil Change International (By Andy Rowell): http://priceofoil.org/2015/03/02/transporting-tar-sands-dangerous-shale-oil/