Trains may be one of the most environmentally capable modes of transportation, but that doesn't mean there isn't still room for improvement. With that in mind, GE has been readying its locomotives for the next generation of emissions standards: Tier 3.

Tier 3 is a continuation of the US Environmental Protection Agency’s program to monitor and lower exhaust emissions by locomotives. It follows, naturally, Tier 0, 1 and 2 emissions standards, and marks a 50 % reduction in acceptable particulate matter levels from Tier 2 levels.

The process of enhancing locomotive emissions standards began with Tier 0: all locomotives built after 1972, be they new or overhauled, must be up to those standards. Then, from 2002-2004, all new locomotives were built to a Tier 1 standard. Locomotives built between 2005 and December 31, 2011 were held to Tier 2 standards—and when it comes time to overhaul those locomotives, they will be brought to the most regulatory level.

The new regulations will be implemented in two phases: on new locomotives built starting in 2012; and starting this year, via overhauls to locomotives that were originally built between 1973 and 2004. Tier 3 locomotives will emit no more than 0.1 grams of particulate matter (PM)—tiny particles that escape from the exhaust after the combustion process—per horsepower hour. Furthermore, they will have maximum nitrogen of oxides (NOx) levels of 5.5 g/bhp·hr.