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Roadside Diesel Emissions Inspection

Clean emissions means your engine is burning fuel efficiently, and that translates into savings for you. Diesel smoke is a major source of public complaints, so a clean engine is good for your business image.

Q. What is the purpose of the New York State Heavy Duty Diesel Emission Program?

A. The 6 NYCRR Part 217-5 heavy duty diesel emission program will identify vehicles that emit excessive smoke and are in need of repair. Nationwide, heavy duty vehicles release about 30 tons of smoke into the air daily. Recent studies conclude that diesel smoke can cause serious health problems. This program is one of New York's initiatives for cleaner air.

Q. How will 'I' be affected?

A. The New York State Roadside Program began June 1, 1999. Heavy duty diesel vehicles with a GVWR more than 8500 lbs. will be subject to testing at roadside inspections. (Buses began June 1, 2000)

The test will typically take 15 minutes to complete. You will receive a copy of the results.

Q. What is OPACITY?

A. Opacity is a measure of the amount of light that cannot pass through a substance, such as the amount of light obstructed as it passes through the exhaust. It is expressed as a percentage.

Q. What is an OPACITY meter?

A. The opacity meter is the unit which samples, at frequent intervals, a representative portion of the exhaust and calculates the amount of smoke coming from the stack.

Q. What if my vehicle does not pass the test?

A. No vehicle will be put out of service for failing a roadside opacity test. The driver may receive a fine that can be reduced if the vehicle is repaired and passes a new opacity test within 30 days.

Keeping your engine tuned to factory specifications will save you money in fuel and corrective repairs and, as a result, you should pass the opacity test.

Q. How is an Opacity Test conducted?

A. The exhaust smoke will be tested with an Opacity Meter using a Snap Acceleration Test.

  • The wheels will be chocked
  • Transmission in neutral
  • Brakes disengaged to activate all emission control equipment
  • The sensor will be inserted to the end of the exhaust stack
  • The accelerator is rapidly depressed and held for a few seconds, then released. This is repeated a minimum of five times.
  • The meter will average three consistent results and create a print out for your records.

Q. What are some common causes of excessive smoke?


  • Clogged or worn fuel filters
  • Restricted air filters
  • Contaminated fuel
  • Oil level overfilled
  • Defective turbocharger
  • Defective or inoperable emissions control devices

Q. What basic repairs can be made to improve the smoke opacity?


  • Adjust emissions control equipment
  • Replace air filter elements
  • Tune up your engine
  • Adjust engine timing
  • Ensure correct operation of cooling system
  • Repair restricted exhaust system

Q. What are the standards that will be used to determine if a vehicle fails?


Standards of Emission Failure
Model Year
1991 or Newer greater than 40%
1974-1990 greater than 55%
1973 or Older greater than 70%

Q. What information will the inspector need from me?

A. It would help the inspection to go quicker if the following information is readily available:

  • Make and year of vehicle
  • Mileage
  • Engine manufacturer
  • Horsepower

For more information contact:

New York State Department of Environmental Conservation
Division of Air Resources
Bureau of Mobile Sources & Technology Development
625 Broadway
Albany, New York 12233-3255
(518) 402-8292

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    625 Broadway
    Albany, NY 12233-3255
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