There are two main classes of railroad locomotives: long-haul and short-haul, or switcher, engines.

Many locomotives in the Houston region used for switching and other short-haul purposes have been replaced with cleaner engines with funding from the Texas Emission Reductions Plan (TERP).

The TCEQ's emissions estimates for container port operations are a subject of some controversy. Its SIP development has assumed one container port would be built, but the US Army Corps of Engineers permitted construction of two facilities.