The combination of electric motors and diesel engines has worked well in locomotives and heavy trucks for years, but carmakers haven't been successful in getting beyond the concept car stage for light duty vehicles. Five years after I started writing about the potential for diesel hybrids, the passenger vehicle market is still relatively quiet -- but that at last may change.

The premium paid for diesel engines and additional cost of an electric motor has scared off auto manufacturers. However, the two powertrains have compelling complementary performance characteristics. For city driving, electric motors (powered by batteries that recapture energy from frequent braking) provide needed acceleration. Diesel engines thrive in comparison to gasoline engines when hauling heavy loads and maintaining highway speeds.

Peugeot says that in 2011 it will bring to Europe the 3008 Hybrid4 sedan. The 2.0 liter engine vehicle is being optimized to minimize carbon emissions, with the company claiming it puts out only as much CO2 as a small city car. The company is also showcasing a plug-in RCZ HYbrid4 Concept Coupe, although that may be more eye candy than reality. Peugeot's sister company, Citroen, will reportedly leverage the technology in the DS5 car, which could arrive in 2011.

BMW is also in the mix with a concept plug-in diesel hybrid with the Mercedes Benz has multiple diesel hybrids in the works, the S 400 BlueHYBRID due out in 2010, the C 300 BlueHYBRID, due out in 2012, and the E 300 BlueHYBRID, which may or may not come to pass.

Now none of these are likely to be high-volume cars aimed at average consumers, but they reflect a growing interest in designing vehicles that don't skimp on performance while achieving great fuel economy. "Performance" hybrids have had mixed success thus far in the U.S. While the Lexus hybrid models have been successful, the Honda Accord Hybrid was a failure, and was discontinued after a few years.

Diesel engines continue to be mostly reserved for the truck and bus lane in the U.S., with the exceptions in 2009 passenger vehicles from Volkswagen, BMW and Audi. If VW has success in reintroducing American buyers to relatively inexpensive diesel vehicles, momentum could shift.

American attitudes toward diesel will need to embrace the new cleaner engines that can be part of the solution to reducing vehicle carbon emissions. Plug-in hybrid diesels when powered by biodiesel could be pitched as the greenest vehicles short of full electric vehicles. That would require a bold vision by one of the automakers that has had success with diesels in Europe.