Union Pacific may have a new use for it's low-emission diesel locomotives. The Omaha-based company has five of the locomotives in service and plans to test them on intermediate-length routes.

The low-emission locomotives were originally built in the 1970s, but they have been re-manufactured with 3,500-horsepower engines. The year-long test will determine what kind of load these locomotives can handle.

UP's transcontinental locomotives are powered with 4,400-horsepower engines. Switch locomotives that are used around the company's rail yards run on 2,000-horsepower engines.