As someone involved in the pipeline industry, it scares me that rail is being considered as a viable alternative. The sheer volume of oil that needs to be moved is enough to overwhelm the rail system. It's also more energy intensive to ship via rail versus a pipeline.

From an environmental perspective, rail has a far higher incident rate than pipelines but has the advantage of having a finite volume to spill. I'm not sure overall which one is considered more "environmentally friendly". I suspect pipelines might have the advantage simply due to the lower incident rate but I don't have any numbers to back this claim.