I am sure that the greenhouse gases from construction pale in comparison to the avoided green house gases from moving the oil via truck. That is why one builds pipelines. They are economically efficient.
Exactly!
Actually, much of this oil is now being moved by tanker rail car. This also is much more expensive than shipping in a pipeline. The other issue with shipping oil in a railcar is that railroads go through towns like Lac-Megantic, PQ. Which on a Saturday night in July 2003 had a fire because an oil train derailed in the center of town. The fire KILLED 47 people.
https://www.bbc.com/news/world-us-canada-42548824