Yesterday we chatted about renting green cars, but what if you want to purchase a green car? Increased fuel efficient vehicles are entering the market all the time and if some in Congress have their way, new requirements that American automakers produce green cars could add many more. Still, it’s up to you to do your homework to find a car which bests suits your driving habits, budget, and shade of green.

For drivers who commute to work long distances driving highway miles without stop and go traffic, an efficient conventional vehicle may be better for you. Sound shocking? It’s not. Most hybrid vehicles generate energy through braking, making them more efficient for city driving than highway driving. If you were, for example, to compare the costs and benefits of purchasing a Honda Civic with that of a Hybrid Honda Civic, you may find that your driving habits do not make the hybrid worth the added costs because you use your car to take long trips with little stop and go. The same can be said if you take public transportation most of the time and drive very few miles.

Take the time to understand hybrid technology so that you can best decide if it’s worth the extra cost based on they type of driving you do and the alternative car you would drive if it weren’t a hybrid.

Besides hybrids, there are other types of fuel efficient, low emissions vehicles on the market or soon to be on the market. Relatively small groups of people are taking it upon themselves to retrofit their cars to accept biodiesel, a fuel which usually comes from used oils such as restaurant frying oil. Soon to be on the market are hybrid plug-in vehicles which offer the same technology as the current hybrid with the addition of a plug to help you get a head start at energizing the electric battery and therefore increasing the number of miles you can drive on each tank of fuel.

Still confused about what cars have the greatest fuel efficiency? The U.S. Environmental Protection Agency (EPA) has a program called SmartWay which might help. Previously focused entirely upon tractor trailer fleets, this new program now offers a green leaf logo which you can look for on consumer cars and trucks. Much like other certification programs, the green leaf shows that these vehicles are more fuel efficient and have cleaner emissions than others on the market. If you already have a car in mind and want to see how it ranks, check out the EPA’s Green Vehicle Guide.

But there is more to consider about your future car than just the emissions and fuel efficiency. While most of us think of are concerned about the emissions at the tailpipe, few realize that there are also toxic emissions from a car’s interior. That “new car” smell isn’t just a clean scent auto manufacturers spray at the end of production; it’s the off gassing of chemicals used to make upholstery, dashboards, the foam in seats, and other interior parts. The Ecology Center offers a project called Healthy Car which tests hundreds of cars and rates them based on their toxicity. The most common chemicals found in cars are flame retardants (found to be endocrine disruptors), lead, and polyvinyl chlorides (PVC). Take a look at the most and least concern vehicles for 2008.

Lastly, more car manufacturers are making a concerted effort to clean up their manufacturing plants by recycling, reducing waste, and eliminating many toxic chemicals. Subaru celebrates their fourth year as a zero waste manufacturer this year. These efforts not only reduce the waste going into landfills but also the chemicals to which workers are exposed.

When purchasing your next vehicle, look at the whole picture, not just what goes in the gas tank and out the tailpipe.