Locomotive builders greeted 2015 with a fleet of engines ready, or being tested for the U.S. Environmental Protection Agency’s Tier 4 standards. The standards were announced in 2008 with a goal of reducing particle emissions by 90 percent and nitric oxide and nitrogen dioxide emissions by 80 percent, compared with 1992 levels.

General Electric was the first to deliver locomotives that met Tier 4 standards. GE is working on producing more than 1,000 locomotives for BNSF Railway from early 2015 to 2017. The first 39 units of the order will be the ET44C4 class, with additional retooling to the production line for newer locomotives.

GE’s main North American competitor, Progress Rail / Electro-Motive Diesel, has been lagging behind in the production of Tier 4 diesels. The once longtime dominator of the domestic diesel market released a pair of SD70Ace-T4 locomotives, with the 12-cylinder type-1010 engine in November for testing at the AAR Transportation Technology Center near Pueblo, Colo.

Another locomotive manufacturer is entering the Tier 4 market. Cummins rebuilt a former Union Pacific EMD SD90MAC with the company's Tier 4 compliant engine: the QSK-95. The one-of-a-kind locomotive is undergoing testing on the Indiana Rail Road.

For the last 10 (business) days of the year, Trains editors will present the Top 10 stories of the year in reverse order starting Dec. 16 and finishing on Dec. 31.