Under Tier 2 standards, vehicles are divided into emissions standards called bins. There are 11 bins currently, ranging from 1 (the cleanest vehicle) to 11 (the most polluting). A bin 1 vehicle is equivalent to a zero-emission vehicle; 5 is the average car (all new vehicles must meet this standard for nitrous oxide emissions) and 11 is applied only to very large trucks [source: GreenerCars.org]. Under Tier 2, light duty trucks like SUVs are also subject to the same emissions standards as passenger cars, regardless of weight.
So, how do you make your car greener? There are several ways.
First, find out how your vehicle is classified according to the emissions standards. An automaker's website will probably have this information, and many cars have the emissions rating on a sticker in the window. All newer cars, however, have a mandatory label under the hood that identifies the emission standard.
Second, get your car inspected each year and make sure it complies with your state's emissions standards. During the inspection, a mechanic will place your car on a dynamometer -- a kind of treadmill for a car that lets it travel at different speeds while staying in place -- with a device hooked up to the tailpipe. Your car will fail the test if it releases an overly high amount of hydrocarbons, carbon monoxide or nitrogen oxides [source: Texas Department of Public Safety].
Besides the fact that the law in many states requires drivers to get a yearly inspection, and that the auto shop will make sure your brakes and other mechanical and electrical components are working correctly while you're there, this test will keep you from driving around in a smog-spewing clunker. What's more, these cars usually get better fuel economy, so you don't have to worry as much about wasteful fuel consumption on the road.
For those looking to purchase a new car or a recently built used car, there are many models available with low emissions in mind. For instance, the Toyota Prius is a bin 3 car, while the Honda Civic Hybrid is even lower at bin 2. Ford's Escape Hybrid is a bin 3 vehicle, which is an impressive rating for an SUV. Under the tough California emissions standards, the non-hybrid Toyota Yaris and Honda Fit are both considered Ultra-Low Emissions Vehicles [source: GreenerCars.org].
Someday we just may all be driving electric or hydrogen-powered cars that don't emit chemicals that harm our health or the environment. But until then, we'll simply have to make do by maximizing our car's fuel efficiency, by learning as much about green driving as we can, and by making sure our older cars don't pollute too much.
For more information regarding emission certification and eco-friendly driving, take a look at the links on the next page.