What Is an Emissions Test?

Emission tests measure how much air pollution a vehicle is producing.
U.S. states require vehicle inspections that test the types and amounts of gases released in the exhaust of a car or truck.
The EGR valve recirculates vapors to help prevent excess pollutants from being released in a car's emissions. It is often tested as part of a vehicle emissions inspection.
Emissions testing is regulated by the Department of Motor Vehicles in each state.
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An emissions test is a required assessment of a vehicle’s pollution output under simulated normal driving conditions. It usually performed by auto mechanics in an auto mechanic shop. Vehicles are connected to a chassis dynamometer, which takes the car though various speed cycles that occur while driving. The dynamometer displays the revolutions per minute (RPM), horsepower, and torque of the engine while the wheels of the vehicle turn rollers located under them. An oxygen sensor measures the amount of pollution released by the car during the test.

At least 15 countries, including the United States, require vehicle emissions tests. Many countries follow similar protocols and have many of the same problems with vehicle emissions and testing. Since air pollution contributes to a decline in the health of a population, different countries often seek to reduce the amount of vehicle pollution that is released into the air. Vehicle emissions testing is designed to identify those vehicles that add too many pollutants to the air.

The Department of Motor Vehicles (DMV) in each state regulates these tests in the United States. The purpose of the testing in the US is to reduce air pollution by refusing to register vehicles that excessively pollute. Driving a car that has failed an emissions test can lead to a fine.


Cars emit the following pollutants into the air: nitrogen oxides, carbon monoxide, volatile organic compounds (VOCs), and fine particulate matter. These pollutants can damage the respiratory systems of people who are constantly exposed to them. By mandating an emissions test, DMVs aim to improve the respiratory health of individuals.

Although the emissions test is required by most states, it is easy for fraudulent testing to occur. Testers can choose to pass the non-passing vehicles by connecting the testing equipment to a passing car rather than the actual car that needs testing. As a result of improper testing, owners are able to operate their high-polluting vehicles on the road without penalty. These vehicles contribute to poor air quality in highly compact urban environments. Some emissions regulations are aimed at penalizing the owners of polluting vehicles.

Emissions tests help reduce air pollution. In urban cities with high traffic volume, lower emissions from cars help to reduce respiratory conditions. Cars that have fewer fumes emanating from them help to create a healthier breathing environment for urban populations. Rural or small town populations generally do not suffer from smog or unhealthy air quality. As a result, some small towns do not have emissions regulations.

In the US, the Environmental Protection Agency (EPA) is the federal agency that regulates vehicle emissions. Although this agency does not conduct emissions testing directly, the EPA does set the standards for vehicle emissions. In addition the EPA provides states with federal funding for low emission vehicle incentives and compliance programs.


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Post 8

@Mor - I think the whole thing is a joke, myself. They have the technology to replace car engines so that they don't have any emissions. They ought to be getting people to do that, rather than just messing around with emissions tests.

Even the cleanest kind of fossil fuel car is still making a lot of pollution. If the government is going to interfere anyway, why not go all the way and solve the problem entirely?

Post 7

@Monika - I agree. I mean, when it comes down to it, if you've got a car that's polluting more than usual, you're harming all the people around you. It's not even the same as smoking, because at least with smoking, the harm is isolated and you can make sure you smoke by yourself.

With cars, by their very nature, you're going out in public and adding to the general pollution there. Raising rates of lung disease and cancer and so forth. If someone just decided to go out and spew a bunch of chemicals into the sky for the fun of it, they would be arrested for causing harm. I don't think car drivers should be held to a different standard. And if a car emission test is annoying, the easy solution to that is to take the bus instead.

Post 5

@betterment - I imagine people who pay for a fraudulent DMV emissions test probably don't think things through that far. They're either short on time, lazy, or just don't have the money to pay to get their car fixed.

Also, I really doubt that people who do the fraudulent tests charge what it would take to actually fix a car. They probably charge way less, which might make that an attractive option for some people.

Either way, we all lose when people do these fraudulent tests, because they result in people driving cars that are polluting the air.

Post 4

I had no idea people at emissions test stations would do fraudulent tests! That's terrible. Also, I kind of don't get it. I imagine they charge money "under the table" to the people who they do the fraudulent tests for. Wouldn't it just make more sense for those people to just pay the money to get whatever is wrong with their cars fixed?

Post 3

@eidetic - Well, nothing that's done by the government is ever really "free." So would you rather pay for it at the location, or pay for it on your taxes? Either way, you're still going to end up paying money to get emissions testing done on your car.

And I don't really think that's a lot to ask. Everyone benefits from cleaner air because of less pollution due to emissions testing. I for one have no problem paying to get an auto emissions test on my car, or going to get the actual test done. The emissions test centers near me have pretty good hours too.

Post 2

I think mandatory emissions testing is ridiculous. And it's a total waste of my time and money. In my state, it's required, and you have to pay to get it done! So I have to find emissions test locations, take time out of my day to go to one, wait in line, get my car tested, and then pay at the end. I hate doing it, and I think it's unfair the state requires me to do it.

At the very least, it should be free!

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