Vehicle Emissions Fact Sheet ( PDF )
Free to download, print & distribute.

The NMA has long been a proponent of remote sensing for air quality standards, preferring it over the “test-everyone” approach embodied in the BAR90, ASM or I/M-240 tests where all motorists must drive their vehicle to the testing station.

Remote sensing offers all of the advantages and none of the drawbacks of centralized, drive-in tests.

The fact is that one out of every ten vehicles is responsible for the same amount of pollution as the other nine combined. This pattern of “gross emitters” is consistent regardless of what form of testing program is in place.

Gross Emitters

  • are vehicles that can be 1 year old or 15 years old. Age isn’t always a factor.
  • are poorly tuned and have emission control systems that are defective or have been tampered with.
  • have poor performance and fuel economy, but otherwise appear like any other vehicle.
  • produce an even greater share of pollutants if they are high-use vehicles (taxis, delivery trucks, etc.)

How do we identify gross emitters now? Most localities where emissions testing is required use some form of I/M (inspection and maintenance) drive-in test on a regular basis. However, there is a lot of room for improvement, and remote sensing provides the answer.

How does a remote sensing system work?

Remote sensing was developed by Dr. Robert Stedman at the University of Denver, Colorado. This system uses one basic principle: certain gases absorb infrared light at different rates. By placing an infrared (IR) light transmitter on one side of the road and aiming its beam into an IR receiver on the other side, when a vehicle drives through the beam, the computer compares the wavelength of the light after it passed through the exhaust plume to the wavelength of the normal IR light. It then calculates the percentage of hydrocarbons (HC), oxides of nitrogen (NOx), carbon dioxide (CO2) and carbon monoxide (CO). If, and only if, your vehicle is over the maximum limits, a camera records your license plate number and the state is notified. (Enforcement actions or penalties depend on state laws.)

Remote sensing devices are being sold or rented commercially now. The average price of a stationary setup is over $90,000, which includes training. If a mobile remote sensing station is desired, the cost is over $140,000. Expensive? You bet. But it’s far cheaper than constructing a slew of drive-in “test-everyone” stations.

Remote sensing system diagram


Specifications of the GM/Hughes RES-100 “Smog Dog”

Operation: System automatically triggers, acquires and records emissions data.
Calibration: Push-button, used twice a day. Gas bottle normally will last one year.
Discrimination: Carbon Monoxide (CO), Carbon Dioxide (CO2), and Hydrocarbons (HC).
Temp. Range: -45° to +125° F.
Accuracy/repeatability: 10%.
Sensitivity: 100 parts per million, <0.01%.
Setup time: 15 minutes.
Power: 110 VAC.
Max. test rate: 3,600 vehicles per hour.
Data storage: Hard disk, floppy disk and magnetic tape.
Violator data storage: Video image of rear license plate, with CO, CO2, HC, time/date and sample number superimposed on image.
Operational features: Transmitter-to-receiver separation of up to 40 feet for camoflaged or hidden operation. Remote console with 100 foot cable.
Other information: The infrared source is eye-safe. Emissions violation threshold is variable. Print-outs available for a variety of information.


Remote Sensing — less than 50 cents per car. | I/M — greater than $10 per car.

Remote Sensing — 3600 cars per hour. | I/M — 10 cars per hour.

Remote Sensing — better than 10%. | I/M — better than 10%.

Remote Sensing — unobtrusive, on-road test. | I/M — everyone must make special trip.

Remote Sensing — no way to cheat. | I/M — advance notice helps cheating.