Guide Transportation & Air Quality

Motor vehicles, engines, and fuels are leading contributors to air pollution in Massachusetts. Learn what the state is doing to make a difference in the quality of the air we breathe. Do your part by driving a clean-running and fuel-efficient vehicle, keeping it maintained, and making smart commuting choices, like using public transit.

By the Numbers

The Vehicles We Drive Produce 40 percent of the nation's smog-causing pollution and more than 25 percent of its greenhouse gas emissions.

Bay Staters, like most Americans, love to drive - and they are driving more cars, minivans, and SUVs more than ever before: some 50 billion miles per year.

Meanwhile, nearly 90 percent of the freight tonnage transported to, from, and across Massachusetts - cargo valued at more than $350 million annually - moves by truck over our roads.

Getting people and things around is an essential part of day-to-day life, not to mention vital to the Massachusetts economy. But it also is a major source of air pollution.

Motor vehicle exhaust not only contributes to the formation of ground-level ozone, the main ingredient in smog, but also contains toxic air pollutants that harm our health and greenhouse gases that contribute to climate change.

But there are a number of solutions within our each. This page describes what the state is doing - and what you can do - to reduce air pollution from motor vehicles and fuels.

Additional Resources for By the Numbers

Vehicle Fuels & Vapor Recovery

Although hybrid and electric vehicles are growing in popularity, most of the 4.6 million cars, trucks, buses, and SUVs registered in Massachusetts are still powered by internal combustion engines that burn fossil fuels.

Gasoline Usually contains ethanol or another additive, is highly evaporative and flammable. In a gas engine, sparks ignite fuel, but combustion is inefficient. A fraction of the fuel powers the vehicle; most is consumed by friction and heat, or emitted as exhaust.
Diesel Fuel Heavier and oilier than gasoline, but not as evaporative or flammable. In a diesel engine, air compression in cylinders ignites fuel. Because diesel has a higher energy density than gas, vehicles running on it deliver better fuel economy.

Both fuels contain mixtures of hydrocarbons - compounds that contain both hydrogen and carbon atoms. In a "perfect" engine, oxygen from the air would convert all of the fuel's hydrogen to water, and carbon to carbon dioxide.

No combustion process is perfect, though, so both gasoline and diesel vehicles have emission control systems that reduce (but don't eliminate) harmful air pollutants.

Emissions also escape into the air when gasoline evaporates during bulk fuel deliveries and vehicle fill-ups at gas stations. The MassDEP Stage I & II Vapor Recovery Program is aimed at reducing these emissions.

See below to learn about federal gasoline and diesel standards, and fuel economy ratings.

Additional Resources for Vehicle Fuels & Vapor Recovery

Vehicle Emissions & Inspections

More than 60 percent of transportation-related emissions come from gasoline-powered private passenger vehicles.

Under the MassDEP Low Emission Vehicle (LEV) Program, most new vehicles with 7,500 or fewer miles on their odometers need to be equipped with factory-installed, California-certified advanced emission control systems in order to be sold and registered in Massachusetts.

Vehicles with on-board diagnostic (OBD) systems manufactured within the last 15 model years are required to pass an annual Massachusetts Vehicle Check emissions and safety test. Inspections are performed at more than 1,800 licensed stations across the state.

Volkswagen Group of America (VW) in 2015 admitted to installing software "defeat devices" in certain diesel passenger vehicles so they would fraudulently pass the emissions test. Massachusetts will receive $75 million in VW court settlement funds to reduce vehicle emissions, electricity the transportation system, and improve air quality in environmental justice communities. MassDEP is accepting input from stakeholders on how to prioritize these investments.

Additional Resources for Vehicle Emissions & Inspections

Engine Idling Reduction

Unnecessary idling - running a vehicle's engine for longer than five minutes when the vehicle is stopped - is against both state law (M.G.L. Chapter 90, Section 16A) and a MassDEP regulation (Section 7.11 of 310 CMR 7.00).

Idling for a long time is a bad idea because it:

  • Pollutes the air more than driving does, worsening smog and global climate change.
  • Exposes people to health risks - and more so if they have heart or lung problems.
  • Can fill the passenger compartment with exhaust that is dangerous to breathe.
  • Wastes fuel and money. The bigger the engine, the higher the cost.
  • Harms vehicles, causing damage to cylinders, spark plugs, and exhaust systems.

MassDEP is working with cities, towns, schools, and transportation companies to reduce unnecessary engine idling across the state. See below to learn more.

Key Actions for Engine Idling Reduction

Additional Resources for Engine Idling Reduction

Drive-Alone Commuting

Even though there are a number of cleaner and more economical alternatives - from riding buses, trains, and ferries to carpooling and ridesharing - many Bay Staters still choose to drive to and from work or school alone. This can add up to traffic gridlock, longer commutes, and unnecessary air pollution.

The MassDEP Rideshare Program requires many businesses and educational facilities across the state to develop plans and set goals for reducing employee and student drive-alone commute trips.

MassRIDES is a free Massachusetts Department of Transportation (MassDOT) program aimed at reducing traffic congestion and improving air quality. It offers resources and solutions to help commuters and employers make smart transportation choices.

    Transit, Highway & Parking Mitigation

    Under its statutory authority to control and reduce transportation-related air pollution, MassDEP is responsible for ensuring that:

    • Boston and the Massachusetts Port Authority limit the availability of commercial parking spaces in certain high-congestion areas of the city,
    • The state Department of Transportation (MassDOT) effectively operates the greater Boston Central Artery/Tunnel ventilation system, and
    • MassDOT reports on specific mass transit system improvements that are needed to improve air quality.

    Follow the link below for related information.

    Additional Resources for Transit, Highway & Parking Mitigation

    State Laws & Regulations

    MassDEP and the Registry of Motor Vehicles share statutory responsibility for ensuring clean air and safe roads in Massachusetts.

    The two agencies jointly administer the Massachusetts Vehicle Check annual emissions test and safety inspection program.

    Additional Resources for State Laws & Regulations

    State Grants & Incentives

    Massachusetts is providing motorists, commercial and municipal fleet managers, and both public and private employers with financial incentives for putting cleaner vehicles on the road and building the infrastructure needed to support them.

    The Department of Energy Resources offers rebates of up to $2,500 for private purchase or lease of zero-emission and plug-in hybrid light-duty vehicles through the Massachusetts Offers Rebates for Electric Vehicles (MOR-EV) program.

    MassDEP administers two grant programs - the Massachusetts Electric Vehicle Incentive Program (MassEVIP) and MassCleanDiesel - aimed at putting more municipal hybrid and electric vehicles on the road, and reducing emissions from diesel vehicles that are already in use, both on the road and off. See Additional Resources below to learn more.

    Additional Resources for State Grants & Incentives

    What You Can Do

    Some of the best ways to prevent air pollution from cars are just common sense.

    • Drive less by combining errands.
    • Carpool if you can.
    • Take the train or bus to work.

    By carpooling every day, you can save up to $3,000 a year on gas, insurance, parking fees, and wear and tear on your car.

    One person using mass transit instead of driving to work for a year keeps about 9 pounds of hydrocarbons, 62 pounds of carbon monoxide, and 5 pounds of nitrogen oxides out of the air.

    There's more:

    • When you're on the road, travel at steady, moderate speeds.
    • Keep your tires properly inflated to reduce fuel consumption by as much as 10 percent.
    • After you fill the tank, check to make sure the gas cap fits tight.
    • Perform routine maintenance according to the manufacturer's instructions.
    • Replace oil and filters at recommended times.
    • Pay attention to a loss in fuel economy. This usually signals an increase in emissions.
    • Watch your vehicle's tailpipe. Black smoke means the fuel injection system needs to be checked. Blue smoke means your engine is burning oil.

    Additional Resources for What You Can Do

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