Canadian National Railway is testing two diesel-electric locomotives retrofitted to run on cheaper and less polluting natural gas, the transportation giant announced Friday.

If the technology proves viable in trials underway on a 300-mile run north of Edmonton to Fort McMurray, the gateway to the oil sands region of northern Alberta, it could help railways significantly reduce their CO2 emissions, CN vice president Keith Creel said in a statement.

"CN launched this locomotive test to explore the use of natural gas as a potential alternative to conventional diesel fuel," he said.

"Natural gas has a lower carbon content compared with diesel fuel, so that locomotives using natural gas -- if the railway technology employing this form of energy ultimately proves viable -- would produce significantly fewer carbon dioxide emissions."

CN retrofitted the diesel engines in two 3,000-horsepower Electro-Motive Diesel SD40-2 locomotives to run on natural gas using conversion kits supplied by Energy Conversions Inc. of Tacoma, Washington.

The retrofitted locomotives use 90 percent natural gas and 10 percent diesel fuel for ignition, and are paired with a specially equipped and protected tank car.

According to Energy Conversions the mixed fuel locomotive will reduce carbon dioxide emissions by 30 percent, and nitrogen oxide emissions by 70 percent over its workspan.

Fueling and maintenance is being done in Edmonton, Alberta.

CN is one of the largest railways in North America, with 33,000 kilometers (20,505 miles) of track in Canada and the United States, and 22,000 employees. The company last year posted earnings of $2.4 billion on revenues of $9 billion.