There is a Keystone pipeline from those North Dakota oil fields down to Cushing, Oklahoma. The direct path of the Keystone XL pipeline doesn't go near North Dakota. I've posted the map of the existing Keystone pipeline plenty of times.
I've also posted export data for gasoline showing we are exporting an amount of gasoline equal to the capacity of the existing Keystone pipeline and that these new exports started as the existing Keystone pipeline started to be used.
There is no evidence the Keystone XL pipeline will be used to bring down the price of petroleum products in America and not just be exported to take over Venezuela and Libyan markets in the Caribbean.
The question becomes, why didn't they just follow the existing Keystone pipeline? It's a longer route, yes, but there's a lot of crude in North Dakota and across the Canadian border in that region. They already have right of way.