What is an Emissions Test?

An emissions test is an assessment of a vehicle’s pollution output under simulated driving conditions. In most cases it can only be performed by auto mechanics with certain specialized equipment and training. Many countries set minimum emissions standards for cars or trucks that are sold within their jurisdictions, and states, provinces, and localities often also require car owners to get tests done every year or every other year in order to be sure that all vehicles using the roads meet these standards. Car engines can emit a range of dangerous gasses as they burn gasoline, and governments have an interest in minimizing these fumes. The test itself is usually pretty easy to perform and usually only takes a few minutes. Results are often automatically reported to government agencies, but falsified tests are nevertheless a problem in some places.

This test is almost always performed in an auto mechanic’s shop or repair garage. Vehicles are connected to a chassis dynamometer, which is a machine that takes the car though various speed cycles that occur while driving. Cars aren’t usually moving while this happens, though; the test is designed to simulate the regular driving experience without actually performing it. Sometimes the wheels of the vehicle turn on rollers located under them, but the car isn’t actually out on the road.

While the engine is going through its rotations, the dynamometer displays the revolutions per minute (RPM), horsepower, and torque of the engine. An oxygen sensor measures the amount of pollution released by the car during the test. The results are usually saved and compiled into a formal “emissions report,” which mechanics use to determine whether the car passes or fails. In some places, mechanics are required to send an official copy of this report to government emissions offices. Motor vehicle agencies sometimes also receive results digitally, often in real time.

At least 15 countries, including the United States, require vehicle emissions tests as a means of limiting and controlling air pollution. The exact testing procedure tends to vary a bit from place to place, and the rules can also be different with respect to how often the tests have to be performed and the levels of toxic emissions that are allowable. Cars will usually fail the test if they emit at levels above the allowable threshold, but what this threshold is, exactly, can change by location. Cars that fail usually have to undergo repairs or else stay off the roads. There may also be a fine levied against drivers whose cars fail.

In the US, the Environmental Protection Agency (EPA) is the federal agency that regulates vehicle emissions. Although this agency does not conduct testing directly, it does set the standards for vehicle emissions. In addition the EPA provides states with federal funding for low emission vehicle incentives and compliance programs. Similar initiatives exist throughout the world as people become increasingly aware of the dangers of vehicle-related pollution.

Cars emit a range of chemicals into the air as a consequence of burning fuel. The most harmful of these include 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, and can also harm the environment. Trees, shrubs, and plants that grow near roadways are often stunted or diseased as a direct consequence of pollution, and a range of animals are also impacted. Environmental protection and public health are usually the biggest goals of emissions testing initiatives.

In urban cities with high traffic volume, lower emission volume from cars helps to reduce respiratory conditions. Cars that have fewer fumes emanating from them, either because their engines are more efficient or because they have special emissions filters installed, can help to create a healthier breathing environment for urban populations.

The emissions test requirement can be easy to circumvent for people bent on breaking the law. Testers can choose to pass what would otherwise be non-passing vehicles by connecting the testing equipment to a passing car rather than the actual car that needs testing. They might also certify results that have been “doctored.” When either of these things happens, owners are may be able to operate high-polluting vehicles on the roads without penalty.