Thanks to the latest diesel engines going to pressurized common-rail direct fuel injection and the use of advanced emission control systems to remove harmful NOx and diesel particulates, the latest diesel-powered buses emit a tiny fraction of the air pollution of older buses. And companies like Cummins, Catepillar, Daimler-Benz, etc. are working on even more advanced technologies that could make diesel engines eventually meet the even more stringent EPA Tier 2 Bin 3 and CARB AT-PZEV standards for exhaust emissions by 2011, an amazing engineering feat.
I’ve driven a turbo diesel car, and those things are @$$-kickin’! If they can solve the emissions problems, and make it so the fuel doesn’t gel in the winter, I’d have to seriously consider one. They’re fast, fun, and efficient. Except of course that the engine’s redline is 4,500 RPM.