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Air Quality

Montgomery County, Department of Transportation (MCDOT) is committed to providing leadership which will foster conservation, protection and improvement of the environment by adopting a MCDOT Environmental Sustainability Policy. MCDOT is an active participant in the regional arena that is charged with improving the region’s air quality and meeting the standards set by the Clean Air Act to reduce harmful emissions that contribute to poor air quality. Read more at the COG website.

The Washington Metropolitan Region’s most serious air pollution problem is ground-level ozone, a harmful gas that is formed when volatile organic compounds (VOCs) and nitrogen oxides (NOx) react with sunlight. Vehicles emit emissions of VOCs and NOx which react chemically in the presence of sunlight to create ground-level ozone ("bad ozone") that results in smog. Sunlight and hot weather produce harmful concentrations of this ozone making it a major summertime air pollutant.

Air Quality
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MCDOT is actively working to improve air quality in several ways:

Congestion and SOVs (single occupancy vehicles) result in higher concentrations of ozone. As shown below, VOC and NOx emissions are greater at lower speeds associated with congestion than at higher speeds associated with more free-flow conditions (35-50 mph). As a result, MCDOT promotes transit, measures to reduce travel during peak periods, and efforts to encourage ridesharing, pedestrian and bicycle modes of transportation.

Reducing Congestion to Improve Air Quality

MCDOT promotes transit and alternatives to reducing car travel during peak periods. During non-peak hours, MCDOT has optimized traffic signal timing at intersections on major corridors and construction of key roads that will not only improve operating speeds (which lowers emissions) but also reduce the length of time existing roads will be in gridlock on a daily basis.

MCDOT has taken initiatives to relieve congestion and grid-lock within the county by implementing and advancing projects and programs that increase roadway capacity and reduce dependency on the private automobile. Emphasis is placed on creating a balanced approach to reducing congestion on the County’s roadways while improving air quality and minimizing the environmental impact of proposed projects.

Projects recommended for implementation are chosen with strong consideration on their ability to reduce congestion by either providing additional lane miles to the existing transportation network or by increasing the viability of transit and other alternative transportation options. One major criterion by which all proposed projects were evaluated was whether that project/program was air quality neutral or whether it had a positive or negative impact on the air quality of the region. (back to top)

Cleaner Emission & Alternate Fuel Vehicles

MCDOT is committed to reducing smog-forming emissions through the purchase of alternate fuel vehicles and vehicles that produce cleaner emissions.

hybrid automobileOlder buses are being replaced with more environmentally friendly buses that run on compressed natural gas (CNG) or hybrid diesel-electric technology. Nearly one-third of the Ride On bus fleet is currently comprised of these “cleaner” buses.
MCDOT is currently piloting bio-diesel fuel for its transit and heavy duty vehicles.
A multi-technology fleet of alternative-fueled vehicles is being piloted in order to benefit from expected improvements in operations, costs, and environmental impacts as these different technologies evolve.

Currently the Country fleet includes the following cleaner emission and/or alternate fuel vehicle:

Ride On bus with bike rack

Alternate Transportation

Montgomery County, being strategically situated in the Washington Metropolitan area, has many transit options available to its residents. These include the MCDOT operated Ride On buses, the regionally operated Metrobus and Metrorail system, and the State operated MARC commuter train.

MCDOT promotes many alternate transportation programs and options including:

Forest and Trees

Since 2001, approximately 46 acres of forest have been planted by the MCDOT adjacent to WSSC’s Triadelphia reservoir.  The reforestation site increases the water quality buffer surrounding the reservoir.

The MCDOT also plants street trees on most new road construction projects. (back to top)

Tree Maintenance

In order to increase the quantity and improve the quality of forests and trees, restore and protect natural forest ecosystems, and enhance the poor condition of street trees in the county’s most developed areas, MCDOT is committed to increase the tree canopy in Montgomery County. Some of the accomplishments include:

Tree Canopy Benefits

Heat from earth is trapped in the atmosphere due to high levels of carbon dioxide (CO2) and other heat-trapping gases that prohibit it from releasing heat into space -- creating the "greenhouse effect." Trees remove CO2 from the atmosphere during photosynthesis to form carbohydrates that are used in plant structure/function and return oxygen back to the atmosphere as a byproduct.

Trees remove other gaseous pollutants such as sulfur dioxide (SO2) (from coal burning for electricity/home heating), ozone (from the emissions of automobiles, nitrogen oxides from automotive emissions), and particulates (emitted in smoke from burning fuel, particular diesel) that enters our lungs and cause respiratory problems by absorbing them in the leaf surface. 

Trees reduce topsoil erosion, prevent harmful land pollutants contained in the soil from getting into our waterways, slow down water run-off, and ensure t hat our groundwater supplies are continually being replenished.

Trees lower local air temperatures by transpiring water and shading surfaces. Because they lower air temperatures, shade buildings in the summer, and block winter winds, they can reduce building energy use and cooling costs.

Trees can also enhance traffic calming measures, such as narrower streets, extended curbs, roundabouts, etc. Tall trees give the perception of making a street feel narrower, slowing people down. (back to top)


The Montgomery County Resource Recovery Facility (RRF) is a waste-to-energy facility that converts the stored internal energy of waste into electricity.  By generating power for use by homes and businesses, this waste-to-energy facility offset the burning of fossil fuels, as well as emissions from coal and oil fired utilities. In fact, combusting 1,000 tons of solid waste saves the burning of about 1,600 barrels of oil or 500 tons of coal.(back to top)


In May, 2007, the Division of Solid Waste Services changed the fuel it uses for all equipment at the Dickerson Compost Facility to B20, a bio-diesel fuel that is 20% based on soybean oil. Environmental benefits of B20 include an estimated 12% reduction in both particulate matter (soot) and carbon monoxide and about 20% reduction in total hydrocarbon emissions, accompanied by only about a 2% increase in nitrogen oxides. (back to top)




For any MCDOT service request or complaint, call 311
When dialing outside of the county, call 240-777-0311 or submit via their website.

For website comments or to report website problems or broken links, please email us. This email address does not handle service requests or complaints.

 Director's Office · Montgomery County Department of Transportation
101 Monroe Street, 10th Floor · Rockville, Maryland 20850 ·
· telephone: 240-777-7170 · fax: 240-777-7178 ·