The proposed Keystone XL pipeline meant to carry heavy crude from Alberta tar sands will be the safest in the United States, company officials said in Montana.The U.S. House of Representatives in July passed a measure that gives the White House until November to finish a review of TransCanada\'s proposed Keystone XL oil pipeline. The current pipeline carries about 590,000 barrels of oil per day from oil sands projects in Alberta, Canada, to markets in the United States.Keystone XL would expand the network from Oklahoma to refineries along the coast of the Gulf of Mexico. The extension would cross dozens of small creeks and streams and run under the Milk, Missouri and Yellowstone rivers as it passes through Montana.Company officials on a visit to Billings, Mont., said design plans include numerous safety features. Les Cherwenuk, a director for the Keystone XL project, said workers would bore 25 feet under major rivers, use emergency shut off valves and incorporate special steel on the pipeline to make it puncture resistant, the Billings Gazette reports.Critics say transporting Alberta crude oil carries significant environmental risk. Workers are examining the affects of a heavy crude spill in Michigan more than a year after a pipeline ruptured there.Billings was the site of a crude oil spill in the Yellowstone River in July.Robert Jones, vice president of TransCanada\'s pipeline division, was quoted as saying, pipelines \"are the safest and most environmentally conscious way of transporting crude oil.\"