EPA Tier 4 emissions standards

Amtrak has issued a request for information concerning 15 new Tier 4 diesel-electric locomotives, as well as one diesel switch yard locomotive.
Railroads and locomotive builders are prepared to meet the EPA's tough Tier 4 emissions standards. Meanwhile, LNG has taken center stage as a potential replacement for diesel fuel.
After an absence of 12 years, Electro-Motive Diesel Inc. (a subsidiary of the Progress Rail Services Corp. division of Caterpillar Inc.’s Rail Division) has reentered the passenger locomotive market.