It may not be soon enough for everyone, but the greening of America’s automobile population is happening. Hybrid cars are here to stay, and more and more of them include innovations such as expanded battery packs that can be recharged from an at-home wall socket. As battery technology improves at a faster pace than ever, look for 100% electric cars in the not-too-distant future.

Another less noticed but equally significant development is the introduction to the USA of flex-fuel vehicles, which can run on ethanol or gasoline, or mixtures of the two. These cars have been driving around for years in Brazil, where you can get 8,000 barrels of ethanol per year per one square mile of refined sugar cane.

Also quietly making its way into the USA is low sulphur diesel fuel, which at 15 PPM sulphur is pretty much as clean as gasoline. Diesel engines are simple to maintain, diesel fuel is simple to refine, and diesel cars get mileage that often is comparable to hybrids, if not better in some cases.

The cars of tomorrow may take on many innovative designs. It may be that as fuel choices and design choices diversify, no single type of fuel or vehicle will dominate. There isn’t enough of any one fuel to go around, be it gasoline, diesel, biodiesel, or ethanol, and we aren’t sure how we’ll manufacture enough hydrogen, or produce enough electricity, for those choices to become our sole fuel. Given these realities, the emerging diversity of green solutions to how we design and fuel our cars is most encouraging.