No such thing as a "green" car, but there are "greener" options

By Amy Westervelt

Unless you've been cut off from all forms of media for the last two years, you're aware of the fact that vehicle transportation is a major contributor to climate change. According to the Environmental Protection Agency (EPA), transportation accounts for 29 percent of total greenhouse gas emissions in the United States. Transportation also is the fastest growing source of emissions, accounting for 47 percent of the net increase in total U.S. emissions since 1990. And that's just getting from point A to point B -- the figures don't factor in the emissions created by manufacturing automobiles or refining fuel.

On top of the environmental cost, the price of gas is not likely to come down too terribly much, and even oil companies’ scientists attest to the fact that we are running out of oil. All of which points to a crucial need for better public transportation and vehicles that are both fuel-efficient and low-emission.

Thanks to our collective century-plus love affair with the automobile, U.S. public transportation systems still have a way to go before the majority of people can reliably get where they need to go without a car. Thankfully, from large automotive companies to small start-ups, we're starting to see a number of choices for fuel-efficient, low-emission automobiles, so much so that it can sometimes be confusing to pinpoint the benefits of each and the differences between them. Following, a simple breakdown of energy-efficient, low-emission vehicles:

Hybrids

Hybrids run off both an internal combustion engine and an electric engine with rechargeable battery. The battery is recharged when the car brakes. Because hybrids switch over to electric power at lower speeds, they make the most of gasoline, getting roughly 40 miles to the gallon, depending on the model. While hybrids have been the poster child for the "green" movement over the last few years, in reality they are only slightly better than conventional vehicles. Because they have two engines, the manufacturing emissions associated with hybrids are higher than those associated with conventional cars; furthermore, there are numerous conventional diesel vehicles in the European Union that get up to 70 miles per gallon.

Plug-in Hybrid Electric Vehicles

The next generation of hybrid vehicles, plug-in hybrids (PHEVs) run primarily off the electric engine and use the combustion engine for back-up. Their batteries are larger and more powerful, enabling them to run for longer without recharging. When they do need to be charged, they can be plugged into an electrical outlet. The result is much higher fuel efficiency, and much lower emissions, than a conventional hybrid. However, the electric engine comes with its own suite of environmental issues - first, it plugs into the grid, and "the grid" for most of us, is still powered by coal-fired power plants, which means your car use is still tied to a large amount of pollution. Then there's the manufacture and disposal of batteries. Finally, manufacturers are still working out the kinks of battery technology, which is why we're not likely to see PHEVs on the road until about 2010. By that time, hopefully more of the grid will be powered by sun and wind.

Electric Vehicles

Fully electric vehicles emit nothing when you're driving them, and get a range of about 120 - 200 miles per charge. Their primary environmental impact come from the electricity used to power them - if you're plugged into a coal-fired grid, there are still emissions associated with your drive. However, as more and more states add larger amounts of renewable energy to the grid, the associated emissions will go down. Currently available models are typically fairly high in cost, but more affordable models are coming on line in the next one to two years from Mitsubishi, GM, Ford, Nissan, and California start-up Tesla, which currently sells its high-end roadster, a fully electric high performance sports car. The manufacture and disposal of batteries, however, especially large batteries produced at a scale to supply all the current car drivers, is still problematic for environmentalists.

Biodiesel-fueled Car

Standard diesel engines can be converted to run on biodiesel -- fuel derived from various plants and/or waste oil from restaurants. There are even DIY converter kits that run about $600 (check out greasecar.com). Biodiesel is not a fossil fuel and is more fuel-efficient than conventional diesel, but it still emits greenhouse gases when burned. According to the EPA, biodiesel emits less CO2 and particulate matter than conventional fuels, but more nitrous oxide, which also is a greenhouse gas.

Hydrogen-fueled Cars and Fuel Cells

For a long time, many believed hydrogen fuel cell cars were the wave of the future. Cars that run off hydrogen fuel cells can feasibly run just as well as currently available vehicles, and emit only water, which could be used for other things (and guess what? we're running short on water these days too). However, there are numerous engineering obstacles to overcome with hydrogen - namely infrastructure (building hundreds of stations stocked with high-pressure hydrogen canisters is hard to imagine), cost (as with most new fuels, cost for hydrogen fuel is currently prohibitive), and safety (there are still concerns about how hydrogen fuel cells would react in an accident). However, companies such as BMW are continuing to make strides in these areas, while electric car proponents argue that the emphasis should be on increasing the range of existent battery technology.