United States emission standards

In the United States, emissions standards are managed on a national level by the Environmental Protection Agency (EPA). State and local governments may apply for waivers to enact stricter regulations.

Motor vehicles

Due to its preexisting standards and particularly severe motor vehicle air pollution problems in the Los Angeles metropolitan area, the U.S. state of California has special dispensation from the federal government to promulgate its own automobile emissions standards. Other states may choose to follow either the national standard or the stricter California standards. States adopting the California standards include Arizona (2012 model year),[1] Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico (2011 model year), New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington, as well as the District of Columbia.[2][3] Such states are frequently referred to as "CARB states" in automotive discussions because the regulations are defined by the California Air Resources Board.

The EPA has adopted the California emissions standards as a national standard by the 2016 model year[4] and is collaborating with California regulators on stricter national emissions standards for model years 2017–2025.[5]

Light-duty vehicles

Light-duty vehicles are certified for compliance with emission standards by measuring their tailpipe emissions during rigorously-defined driving cycles that simulate a typical driving pattern. The FTP-75 city driving test (averaging about 21 MPH) and the HWFET highway driving test (averaging about 48 MPH) are used for measuring both emissions and fuel economy.

Two sets, or tiers, of emission standards for light-duty vehicles in the United States were defined as a result of the Clean Air Act Amendments of 1990. The Tier I standard was adopted in 1991 and was phased in from 1994 to 1997. Tier II standards are being phased in from 2004 to 2009.

Within the Tier II ranking, there is a subranking ranging from BIN 1–10, with 1 being the cleanest (Zero Emission vehicle) and 10 being the dirtiest. The former Tier 1 standards that were effective from 1994 until 2003 were different between automobiles and light trucks (SUVs, pickup trucks, and minivans), but Tier II standards are the same for both types.

These standards specifically restrict emissions of carbon monoxide (CO), oxides of nitrogen (NOx), particulate matter (PM), formaldehyde (HCHO), and non-methane organic gases (NMOG) or non-methane hydrocarbons (NMHC). The limits are defined in grams per mile (g/mi).

Phase 1: 1994–1999

Were phased in from 1994 to 1997, and were phased out in favor of the national Tier 2 standard, from 2004 to 2009.

Tier I standards cover vehicles with a gross vehicular weight rating (GVWR) below 8,500 pounds (3,856 kg) and are divided into five categories: one for passenger cars, and four for light-duty trucks (which include SUVs and minivans) divided up based on the vehicle weight and cargo capacity.

California's Low-emission vehicle (LEV) program defines six automotive emission standards which are stricter than the United States' national Tier regulations. Each standard has several targets depending on vehicle weight and cargo capacity; the regulations cover vehicles with test weights up to 14,000 pounds (6,350 kg). Listed in order of increasing stringency, the standards are:

The last category is largely restricted to electric vehicles and hydrogen cars, although such vehicles are usually not entirely non-polluting. In those cases, the other emissions are transferred to another site, such as a power plant or hydrogen reforming center, unless such sites run on renewable energy.

Transitional NLEV: 1999–2003

A set of transitional and initially voluntary "national low emission vehicle" (NLEV) standards were in effect starting in 1999 for northeastern states and 2001 in the rest of the country until Tier II, adopted in 1999, began to be phased in from 2004 onwards. The National Low Emission Vehicle program covered vehicles below 6,000 pounds GVWR and adapted the national standards to accommodate California's stricter regulations.

Phase 2: 2004–2009

Instead of basing emissions on vehicle weight, Tier II standards are divided into several numbered "bins". Eleven bins were initially defined, with bin 1 being the cleanest (zero-emission vehicle) and 11 the dirtiest. However, bins 9, 10, and 11 are temporary. Only the first ten bins were used for light-duty vehicles below 8,500 pounds GVWR, but medium-duty passenger vehicles up to 10,000 pounds (4,536 kg) GVWR and to all 11 bins. Manufacturers can make vehicles which fit into any of the available bins, but still must meet average targets for their entire fleets.

The two least-restrictive bins for passenger cars, 9 and 10, were phased out at the end of 2006. However, bins 9 and 10 were available for classifying a restricted number of light-duty trucks until the end of 2008, when they were removed along with bin 11 for medium-duty vehicles. As of 2009, light-duty trucks must meet the same emissions standards as passenger cars.

Tier II regulations also defined restrictions for the amount of sulfur allowed in gasoline and diesel fuel, since sulfur can interfere with the operation of advanced exhaust treatment systems such as selective catalytic converters and particulate filters. Sulfur content in gasoline was limited to an average of 120 parts-per-million (maximum 300 ppm) in 2004, and this was reduced to an average 30 ppm (maximum 80 ppm) for 2006. Ultra-low sulfur diesel began to be restricted to a maximum 15 ppm in 2006 and refiners are to be 100% compliant with that level by 2010.

Phase 3A: 2010–2016

In 2009, President Obama announced a new national fuel economy and emissions policy that incorporated California's contested plan to curb greenhouse gas emissions on its own, apart from federal government regulations.

The combined fleet fuel economy for an auto manufacturer of cars and trucks with a GVWR of 10,000 lbs or less will have to average 35.5 mpg. The average for its cars will have to be 42 mpg, and for its trucks will be 26 mpg by 2016, all based upon CAFE Standards.[6] If the average fuel economy of a manufacturer's annual fleet of vehicle production falls below the defined standard, the manufacturer must pay a penalty, currently $5.50 USD per 0.1 mpg under the standard, multiplied by the manufacturer's total production for the U.S. domestic market.[7] This is in addition to any Gas Guzzler Tax, if applicable.[8]

A second round of California standards, known as Low Emission Vehicle II, is timed to coordinate with the Tier 2 rollout.

The PZEV and AT-PZEV ratings are for vehicles which achieve a SULEV II rating and also have systems to eliminate evaporative emissions from the fuel system and which have 150,000-mile/15-year warranties on emission-control components. Several ordinary gasoline vehicles from the 2001 and later model years qualify as PZEVs.

If a PZEV has technology that can also be used in ZEVs like an electric motor or high-pressure gaseous fuel tanks for compressed natural gas (CNG) or liquified petroleum gas (LPG), it qualifies as an AT-PZEV.

Heavy-duty vehicles

Further information: Not-To-Exceed – EPA diesel standards

Heavy-duty vehicles must comply with more stringent exhaust emission standards and requires ultra-low sulfur diesel (ULSD) fuel (15 ppm maximum) beginning in 2007.[9] Since 2007 only diesel models are allowed in the heavy duty class; the EPA banned gasoline models in 2007.

Greenhouse gases

Further information: Global Warming Solutions Act of 2006 (California)

Federal emissions regulations do not cover the primary component of vehicle exhaust, carbon dioxide (CO2). Since CO2 emissions are proportional to the amount of fuel used, the national Corporate Average Fuel Economy regulations are the primary way in which automotive CO2 emissions are regulated in the U.S. However, the EPA is facing a lawsuit seeking to compel it to regulate greenhouse gases as a pollutant.

As of 2007, the California Air Resources Board passed strict greenhouse gas emission standards[10] which are being challenged in the courts.[11]

On September 12, 2007, a judge in Vermont ruled in favor of allowing states to conditionally regulate greenhouse gas (GHG) emissions from new cars and trucks, defeating an attempt by automakers to block state emissions standards. A group of automakers including General Motors, DaimlerChrysler, and the Alliance of Automobile Manufacturers had sued the state of Vermont in order to block rules calling for a 30 percent reduction in GHG emissions by 2016. Members of the auto industry argued that complying with these regulations would require major technological advances and raise the prices of vehicles as much as $6,000 per automobile. U.S. District Judge William K. Sessions III dismissed these claims in his ruling. "The court remains unconvinced automakers cannot meet the challenge of Vermont and California's (greenhouse gas) regulations," he wrote.

Meanwhile, environmentalists continue to press the Administration to grant California a waiver from the EPA in order for its emissions standards to take effect. Doing so would allow Vermont and other states to adopt these same standards under the Clean Air Act. Without such a waiver, Judge Sessions wrote, the Vermont rules will be invalid.[12][13][14][15]

Consumer ratings

Air pollution score

EPA's air pollution score[16] represents the amount of health-damaging and smog-forming airborne pollutants the vehicle emits. Scoring ranges from 0 (worst) to 10 (best). The pollutants considered are nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), formaldehyde (HCHO), and various hydrocarbon measures – non-methane organic gases (NMOG), and non-methane hydrocarbons (NMHC), and total hydrocarbons (THC). This score does not include emissions of greenhouse gases (but see Greenhouse gas score, below).

Greenhouse gas score

EPA's greenhouse gas score[16] reflects the amount of greenhouse gases a vehicle will produce over its lifetime, based on typical consumer usage. The scoring is from 0 to 10, where 10 represents the lowest amount of greenhouse gases.

The Greenhouse gas score is determined from the vehicle's estimated fuel economy and its fuel type. The lower the fuel economy, the more greenhouse gas is emitted as a by-product of combustion. The amount of carbon dioxide emitted per liter or gallon burned varies by fuel type, since each type of fuel contains a different amount of carbon per gallon or liter.

The ratings reflect carbon dioxide (CO2), nitrous oxide (N20) and methane (CH4) emissions, weighted to reflect each gas' relative contribution to the greenhouse effect.

Non-road engines

Non-road engines, including equipment and vehicles that are not operated on the public roadways, are used in an extremely wide range of applications, each involving great differences in operating characteristics and engine technology. Emissions from all non-road engines are regulated by categories.[17]

In the United States, the emission standards for non-road diesel engines are published in the US Code of Federal Regulations, Title 40, Part 89 (40 CFR Part 89). Tier 1-3 Standards were adopted in 1994 and was phased in between 1996 and 2000 for engines over 37 kW (50 hp). In 1998 the regulation included engines under 37 kW and introduced more stringent Tier 2 and Tier 3 standards which was scheduled to be phased in between 2000 and 2008. In 2004, US EPA introduced the more stringent Tier 4 standards which was scheduled to be phased in between 2008 and 2015. The testing cycles used for certification follow the ISO 8178 standards.

Small engines

Pollution from small engines, such as those used in gas-powered groundskeeping equipment reduces air quality. Emissions from small offroad engines are regulated by the EPA.[18] Specific pollutants subject to limits include hydrocarbons, carbon monoxide, and nitrogen oxides.[19]

Electricity generation

Performance-based regulation of greenhouse gases from electricity generation has been initiated on the state level. California was the first to implement this standard in January 2007 by adopting Senate Bill 1368, which set a limit of 1,100 lbs. CO2 per megawatt-hour on "new long-term commitments" for baseload power generation.[20] This legislation was intended to apply to new plant investments (new construction), new or renewal contracts with a term of five years or more, or major investments by the electrical utility in its existing baseload power plants.[20] The number of 1,100 lbs. CO2/MWhr corresponds to the emissions per electrical output of a combined cycle gas turbine plant. By comparison, coal-fired steam turbine plants produce 2,200 lbs. CO2/MWhr or more.[21] Other western states followed suit soon after California, with Oregon, Washington, and Montana passing similar bills into law later that year.[22]

Air quality standards

Individual states with areas that do not attain the targets set by the EPA in the National Ambient Air Quality Standards must promulgate specific regulations which reduce the corresponding emissions from local sources.

State emission testing

State Emissions
Name Light duty gasoline Emissions testing Light-duty diesel Emissions testing Heavy-duty diesel Emissions testing Special notes
Alabama[23] No emissions testing required No emissions testing required Alabama maintains "volunteer emission testing"
Alaska [24] ≥6 model years old (Anchorage) Every two years Exempt Exempt
Arizona [25][26] Model Years ≥1967 but more than 5 model years old (Pima County/ Maricopa County) Every two years 1967–2007 (Pima County/ Maricopa County) Pima County: 30 percent opacity

Maricopa County: 20 percent opacity

Maricopa County J1667 test protocol

Model year <1991: 55 percent opacity
Model year ≥1991: 40 percent opacity

Only state which still conduct emission testing dating back to the 1967 model year unlike other states using EPA classification (a few still conduct test for 1968-present (1968+ testing is for jurisdictions using defined EPA standards for vehicle classification since the '68 model year and beyond automobiles must have an exhaust emission system - PCV system, air injection pump, controlled spark module) e.g. the absence of a rolling chassis exemption - in some states when an automobile reaches an age limit (as in 25 model years old) the vehicle is exempted or pertaining to motor vehicle laws e.g. classic automobile registration and displaying vintage license plates
California vehicles 1976 and newer model-year gas-powered, hybrid, and flex-fuel vehicles; exemptions: new car = ≤6 model-years old are exempt; change of ownership = ≤4 model-years old are exempt required biennialy for registration renewal; 2000 model-year and newer receive only visual and OBDII inspections vehicles 1998 and newer model-year diesel-powered vehicles with a GVWR ≤14,000 pounds; exemptions: none applicable to diesel-powered vehicles required biennialy for registration renewal; 1998 model-year and newer receive only visual and OBDII inspections California-based fleets of 2 or more heavy-duty vehicles with a GVWR >14,000 pounds Periodic Smoke Inspection Program (PSIP) an annual smoke and tamper self-inspection; exemptions: new vehicle = ≤4 model-years old are exempt Prior to 2004 emission testing included 1966 and newer model year automobiles - 1984 calendar year phased in the use of an acceleration simulated mode test criteria - a 1998 state law made pre-1973 automobiles exempt from emission testing where it temporarily included a 30 year rolling chassis exemption which was repealed in 2006 where 1976 and newer are subjected to state mandated emission testing - California visual inspection strictest in the USA (also similar to Japanese 'Shaken' vehicle laws which is their equivalent of vehicle inspection) which serves as a model for other states implementing I/M (inspection/maintenance) programs
Colorado[27] Vehicles older than 4 years required, this will change to 7 years in 2015. Specially registered cars made before 1975 and special vehicles may be exempted. Every two years when required Exempt for first four years of new cars. When outside exemption, passenger cars model year 2004 and newer - every 2 years, else every year. Exempt for first four years of new trucks. When outside exemption, trucks less than 10 years - every two years, else every year. Only on high population corridor encompassing Castle Rock to Wellington, including Boulder and Greeley. Required for vehicles used in this area. Dynamometer testing used.
Connecticut[28] more than 4 model years old but less than 25 model years old Every two years (OBDII) more than 4 model years old but less than 25 model years old Every two years Exempt
Delaware[29] Over 5 model years old Every two years (OBDII)
Georgia Annually (Atlanta metro area only)
Illinois Every two years, after the vehicle is four years old Required only in the Chicago metropolitan area and eastern suburbs of St. Louis, Missouri
Maryland Hybrid vehicles that achieve an EPA gas mileage rating of at least 50 miles per gallon are exempt from testing for 3 years after their model year, after which they are then tested at the standard two year intervals. Every two years
Massachusetts [30][31] Every year OBDII Every year OBDII 8,501 to 14,000 lbs (Medium duty)

14,000 lbs+ (Heavy duty)

Medium Duty: OBDII

Heavy duty: J1667 Protocol

New Hampshire
New Jersey
New Mexico[32][33] Model Years ≥1978 but more than 4 model years old (Bernalillo County) Every two years and at change of ownership Model Years ≥1978 but more than 4 model years old (Bernalillo County) Every two years and at change of ownership Exempt
New York
North Carolina
North Dakota
Ohio More than 4 model years old but less than 25 model years old in the Greater Cleveland area[34] Every two years (OBDII) More than 4 model years old but less than 25 model years old in the Greater Cleveland area Every two years (OBDII) Testing was also required in the Cincinnati and Dayton Metropolitan areas from 1995-2005
Oregon[35][36] Vehicles must be tested every other year for registration renewal in the Portland and Medford areas. Model Years ≥1975 must be tested in Portland area, and those 20 model year and newer in Medford area. Also all vehicles new to Oregon. Every two years Same intervals and exemptions as gasoline cars, 8,500 lbs or less Every two years ≥8,501 lbs Exempt
Rhode Island [37][38][39] more than 2 models years old (inclusive) or 24,000 miles (inclusive) Every two years (OBDII) Exempt Exempt Effective July 2012, any state contracted job requiring heavy duty vehicles must be operated with pollution control devices
South Carolina
South Dakota
Tennessee[40] Any gasoline vehicle with a model year of 1975 and newer and a GVWR of 10,500 lbs or less. Motorcycles are exempt. Annual testing. OBDII + catalytic converter tamper check + fuel cap leak test for 1996 or later vehicles. Tailpipe/tampering testing for 1995 and older vehicles. Any diesel vehicle with a model year of 1975 and newer and a GVWR of 10,500 lbs or less. Annual testing. OBDII + catalytic converter tamper check + fuel cap leak test for 2002 or later vehicles. Curb Idle-opacity/tampering testing for 2001 and older vehicles. Exempt Only applies to Hamilton (Chattanooga), Davidson, Rutherford, Sumner, Williamson, and Wilson (all part of Greater Nashville area) Counties. Required for registration renewal. Davidson county runs their own emissions programs/facilities with the assistance of the state. Shelby County (Memphis) formerly required testing, but ended their program in July 2013 due to funding issues and no state support.[41]
Texas more than 2 model years old to 24 model years old; motorcycles, diesel-powered, and automobiles 25 model years or older exempt from emission testing - includes motor vehicles registered as an Antique or Classic under Texas law (either displaying state-mandated vanity license plate or vintage-era license plates (this also includes past general issue plates from 1975-present with validation stickers used prior to the 1995-present windshield sticker; license plate law in Texas (effective since May 1988) requires new general issue plates after it reaches 8 years of age) annually (both OBDII for 1996–present and ASM to 1995 for motor vehicles registered in the DFW Metroplex and Houston Metro area except for 4-wheel drive/all wheel drive powertrains (4WD/AWD including vehicles over 8500 GVW are subjected to the two-speed idle (TSI) testing; TSI testing to 1995 only in El Paso, Travis, and Williamson Counties) Emission testing mandated for motor vehicles registered in the Houston Metropolitan area (Brazoria, Fort Bend, Galveston, Harris, Montgomery), DFW Metroplex (Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, Tarrant), Austin Metropolitan area (Travis, Williamson) and El Paso counties; since March 1, 2015 inspection stickers no longer issued where an automobile must pass the safety or emission test prior to renewing automobile registration
Virginia[42] more than 2 model years old to 24 model years old Every two years. First-time registrations exempt if vehicle has received an emissions certificate from certain states within previous 12 months. newer than 1996 model year every two years GVWR > 8500 lbs. exempt Emission testing mandated for motor vehicles registered in the counties of Arlington, Fairfax, Loudoun, Prince William, or Stafford, and the cities of Alexandria, Fairfax, Falls Church, Manassas or Manassas Park. Certain hybrids exempt.
Washington[43][44][45][46] Vehicles tested every other year depending on model year. Vehicles model year 2009 and newer and those ≤25 model years old are exempt from testing. (Clark, King, Pierce, Snohomish and Spokane counties). Every two years. Odd model years on odd test years, even model years on even test years. Exempt after 25 years. All diesel passenger vehicles are exempt if weight is under 6,000 lbs. Vehicles > 6,000 lbs and older than 2007 require testing. 2007 and newer exempt regardless of weight. Every two years. Odd model years on odd test years, even model years on even test years. Exempt after 25 years. Emission testing required for most of Clark, King, Pierce, Snohomish and Spokane counties. Vehicles exempt from testing are Motorcycles, 2009 and newer model vehicles, Hybrids that attain greater than 50 miles per gallon city, all diesel passenger vehicles under 6,001 lbs GVWR, all diesel vehicles model year 2007 and newer regardless of weight.
West Virginia
Wisconsin[47] Testing required for vehicles model years 1996 and later in Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha counties (model years 1996 to 2006 up to 8,500 pounds; model years 2007 or newer up to 14,000 pounds) () Every other year before registration renewal; after transfer of ownership; after registration in Wisconsin Testing required for vehicles model years 1996 and later in Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha counties: Model years 2007 and newer which have a gross vehicle rating up to 14,000 pounds Every other year before registration renewal; after transfer of ownership; after registration in Wisconsin Greater than 14,000 lbs. Exempt

See also


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  2. "US EPA approves California auto emissions standard". Reuters. June 30, 2009. Retrieved March 3, 2011.
  3. Daniel Patrascu (July 1, 2009). "EPA Approves California Emission Standard". Autoevolution. Retrieved March 3, 2011.
  4. "EPA and NHTSA Finalize Historic National Program to Reduce Greenhouse Gases and Improve Fuel Economy for Cars and Trucks". April 2010. Retrieved March 3, 2011.
  5. "Regulations & Standards | Transportation and Climate". Epa.gov. Retrieved 2012-10-22.
  6. "Obama: CAFE increase to national standard of 35.5mpg by 2016". autoblog.com. Retrieved 2009-05-19.
  7. Corporate Average Fuel Economy
  8. "Gas Guzzler Tax". Fuel Economy | US EPA. US EPA. Retrieved 11 November 2014.
  9. "2007 Progress Report: Vehicle and Engine Compliance Activities (EPA-420-R-08-011)" (PDF). Retrieved 2011-02-02.
  10. See California Air Resources Board for more information and references.
  11. "News Release: 2004-09-24 ARB Approves Greenhouse Gas Rule". Arb.ca.gov. 2004-09-24. Retrieved 2011-02-02.
  12. http://www.detnews.com/apps/pbcs.dll/article?AID=/20070912/UPDATE/709120456/1148/AUTO01
  13. "Judge rejects automakers' bid to scrap state emission rules : Rutland Herald Online". Rutlandherald.com. 2007-09-12. Retrieved 2012-10-22.
  14. "United States District Court District of Vermont". Archived from the original on September 15, 2007. Retrieved September 17, 2007.
  15. "Carmakers Defeated On Emissions Rules". Washingtonpost.com. 2007-09-13. Retrieved 2012-10-22.
  16. 1 2 "About EPA's Ratings". Epa.gov. 2006-06-28. Retrieved 2011-02-02.
  17. "Nonroad Engines, Equipment, and Vehicles". US EPA. Retrieved 25 December 2013.
  18. 40 CFR §90
  19. 40 CFR §90.103
  20. 1 2 "PUC Sets GHG Emissions Performance Standard To Help Mitigate Climate Change". Docs.cpuc.ca.gov. 2007-01-25. Retrieved 2011-02-02.
  21. ":: CLINTON GLOBAL INITIATIVE :: CGI Member Commitments:". Commitments.clintonglobalinitiative.org. Retrieved 2011-02-02.
  22. "Latest News: The Pew Center on Global Climate Change". Pewclimate.org. 2011-01-25. Retrieved 2011-02-02.
  23. "Motor Vehicle Division - Registration FAQs". Ador.state.al.us. Retrieved 2012-10-22.
  24. "Emission Inspections and Waiver Information". Doa.alaska.gov. Retrieved 2012-10-22.
  25. "ADEQ: Air Quality Division: Vehicle Emissions: What Vehicles Need to be Tested?". Azdeq.gov. Retrieved 2012-10-22.
  26. "ADEQ: Air Quality Division: Vehicle Emissions: Diesel Vehicles". Azdeq.gov. 1997-01-01. Retrieved 2012-10-22.
  27. "Air Care Colorado Program Website".
  28. "CT Emissions Program - FAQs - Testing". Ctemissions.com. 2003-03-17. Retrieved 2012-10-22.
  29. "Vehicle Services Exhaust Emission Inspection". State of Delaware. Retrieved 27 March 2012.
  30. "Massachusetts Vehicle Check". Massvehiclecheck.com. Retrieved 2012-10-22.
  31. "Background Document and Technical Support for Public Hearings on the Proposed Amendments to the State Implementation Plan for Ozone" (PDF). Commonwealth of Massachusetts, Department of Environmental Protection. February 2007. Retrieved 2012-10-22.
  32. "Emissions Testing". New Mexico, Motor Vehicle Division. Retrieved 2012-10-22.
  33. "Emissions testing is required of motor vehicles registered or commuting in Bernalillo County". City of Albuquerque. Retrieved 2012-10-22.
  34. "Which Vehicles Must Be Tested". www.epa.state.oh.us. Retrieved 2016-09-26.
  35. "DEQ Emissions Testing". Oregon DMV. Retrieved 2016-01-12.
  36. "Air Quality: Vehicle Inspection Program (VIP)". Retrieved 2016-01-12.
  37. "Official Manual Motor Vehicle Inspections" (PDF). www.dmv.ri.gov. Retrieved 2012-10-22.
  38. "Rhode Island Diesel Pollution Initiative: Protecting Clean Air in the Ocean State". Clean Water Action. Retrieved 2012-10-22.
  39. "Emissions in Rhode Island... - Diesel Forum". TheDieselStop.com. 2005-11-22. Retrieved 2012-10-22.
  40. "Vehicle Inspection Program". www.tn.gov. Retrieved 2013-11-03.
  41. "City emissions testing soon no more?". http://www.myfoxmemphis.com/. Retrieved 2013-11-03. External link in |publisher= (help)
  42. "Emissions Inspections". Virginia Department of Motor Vehicles. Retrieved 2013-03-29.
  43. "WA Emissions Inspections". Washington State Department of Licensing. Retrieved 2014-01-23.
  44. "emissiontestwa website". Applus+ Technologies, Inc. Retrieved 2014-01-23.
  45. "Frequently Asked Questions: Where is Testing Required?". Applus+ Technologies, Inc. Retrieved 2016-01-12.
  46. "RCW 46.16A.060 Registration—Emission control inspections required—Exemptions—Educational information—Rules.". Washington State Legislature. Retrieved 2016-01-12. line feed character in |title= at position 15 (help)
  47. "Vehicle emission testing". Wisconsin DMV. Retrieved 2014-04-15.

External links

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