California traditionally relishes its leadership in the green movement, and now commuter rail efficiency is no exception. The state's latest aggressive policy to cut carbon loads to 1990 levels by 2020 spurred a major Amtrak overhaul. This week, Amtrak unleashed a new friend to Mother Nature in Locomotive No. 2015 -- a retrofitted engine that chugs along its Capital Corridor line between Sacramento and San Jose. According to the San Francisco Chronicle, the train (which reduces diesel exhaust by nearly 50 percent) is now the cleanest passenger train in California.

Engineers retrofitted the existing engine with high-tech power assemblies, water pumps and radiators rather than purchase a new engine. The revamp, at just over $850,000, was more economical than a new, $3 million engine. In fact, according to the Chronicle, Amtrak plans to retrofit another 14 engines that run along the Corridor over the next few years.

This current project was paid for by the Bay Area Air Quality Management District, the EPA, and the Sacramento Metro Air Quality Management District, which partnered earlier this year to retrofit trucks "that serve the port of Oakland." The groups are concerned with air pollution leading to respiratory disease (among other problems), in addition to greenhouse gas emissions.

These agencies will combine their resources with $2.5 million in federal funds to retrofit the other trains and also stress the importance of improving freight train engines.