The State Department analysis for the first time evaluated two options using rail: shipping the oil on trains to existing pipelines or to oil tankers. The report shows that those other methods would release more greenhouse gases that contribute to global warming than the pipeline. The Keystone XL pipeline, according to the report, would release annually the same amount of global warming pollution as 626,000 passenger cars.
A scenario that would move the oil on trains to mostly existing pipelines would release 8 percent more greenhouse gases such as carbon dioxide than Keystone XL. That scenario would not require State Department approval because any new pipelines would not cross the U.S border.
Another alternative that relies mostly on rail to move the oil to the Canadian west coast, where it would be loaded onto oil tankers to the U.S. Gulf Coast, would result in 17 percent more greenhouse gas emissions, the report said.
In both alternatives, the oil would be shipped in rail cars as bitumen, a thick, tar-like substance, rather than as a liquid.
The State Department was required to conduct a new environmental analysis after the pipeline's operator, Calgary-based TransCanada, changed the project's route though Nebraska. The Obama administration blocked the project last year because of concerns that the original route would have jeopardized environmentally sensitive land in the Sand Hills region.
The administration later approved a southern section of the pipeline, from Cushing, Okla., to the Texas coast, as part of what Obama has called an "all of the above" energy policy that embraces a wide range of sources, from oil and gas to renewables such as wind and solar.
The draft report issued Friday begins a 45-day comment period, after which the State Department will issue a final environmental report before Secretary of State John Kerry makes a recommendation about whether the pipeline is in the national interest.
Kerry has promised a "fair and transparent" review of the plan and said he hopes to decide on the project in the "near term." Most observers do not expect a decision until summer at the earliest.
Canadian Natural Resource Minister Joe Oliver said Friday that Canada will respect the U.S. review process and noted the importance of the pipeline to the Canadian economy.
Obama's initial rejection of the pipeline last year went over badly in Canada, which relies on the United States for 97 percent of its energy exports.
Associated Press writers Rob Gillies in Toronto and Dina Cappiello in Washington contributed to this report.
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