Ship emissions are a growing part of the air pollution problem in the Houston region. Ships often use relatively dirty, older model diesel engines. Emissions standards are lax for even newer model engines, since ships are generally flagged in foreign countries with lax emission standardds.

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 Texas Emission Reduction Plan is one of the most efficient pollution control programs in the Houston region, and must be continued and expanded if Houston is to achieve clean air. Although cost-effective, the TERP is going to fall well short of the binding commitment made to achieve 38.9 tons per day of nitrogen oxide (NOx) emissions reduction in 2007. As of August 2006, the TCEQ reports only 17.7 tons per day of NOx reduction through the TERP, with no further scheduled grants to be awarded. Texas has met only 46% of its commitment to achieve pollution reductions through the TERP.