Best Practices for Reducing 

Near-Road Pollution 

Exposure at Schools

November 2015
c
Best Practices for Reducing 

Near-Road Pollution 

Exposure at Schools

U.S. Environmental Protection Agency

EPA would like to acknowledge the following organizations 

that provided comments on an earlier draft of this document:

South Coast Air Quality Management District

Southern California Green, Clean and Healthy Schools Partnership
Contents

Introduction ..................................................................................................................1

Reducing Near-Road Pollution Exposure at Schools ..........................................2

Near-Road Air Pollution and Children’s Health .................................................................................... 2

How Can Near-Road Pollution Exposure Be Reduced in Schools? ............................................... 3

Building Design and Operation Strategies for Reducing 

Near-Road Pollution Exposure.................................................................................................................... 3

Ventilation, Filtration, and Indoor Air Quality in Schools .............................................................................3

Passive/Natural Ventilation.....................................................................................................................................4

Mechanical Ventilation.............................................................................................................................................4

Filtration.........................................................................................................................................................................5

Actions for Building Occupants...............................................................................................................................7

Summary .........................................................................................................................................................................8

Site-Related Strategies for Reducing Near-Road Pollution Exposure.......................................... 9

Transportation Policies................................................................................................................................................9

Establish Anti-Idling and Idle Reduction Policies ..........................................................................................9

Upgrade Bus Fleets....................................................................................................................................................9

Encourage Active Transportation.......................................................................................................................10

Site Location and Design ........................................................................................................................................10

Roadside Barriers........................................................................................................................................................12

Sound Walls................................................................................................................................................................12

Vegetation...................................................................................................................................................................13

Summary of Recommendations............................................................................ 14

School Ventilation and Filtration System Assessment..................................... 15

Additional Resources ............................................................................................... 16
Introduction

Purpose of This Publication

This publication can help school communities identify 

strategies for reducing traffic-related pollution 

exposure at schools located downwind from heavily 

traveled roadways (such as highways), along corridors 

with significant trucking traffic, or near other traffic or 

vehicular pollution sources. Many of these strategies 

are already being used by schools across the country 

to reduce exposures to traffic-related air pollution. 

We hope that this compilation of best practices will 

help other schools that want to take steps to address 

concerns about traffic-related pollution exposure. 

Many of the best practices outlined in this publication 

may also be effective in reducing exposure at schools 

near other sources of particulate air pollution, such as 

rail yards, ports, and industrial facilities. 

Contact your state or local air pollution agency 

for assistance in evaluating the impacts, if any, that 

traffic-related air pollution may have on your school. 

EPA’s School Siting Guidelines also include information 

on evaluating impacts of nearby sources of air 

pollution. Evaluating the potential impact of trafficrelated air pollution may be performed as part of an 

overall environmental evaluation for your school.

Intended Audience

This publication was designed for school 

administrators, facility managers, school staff, 

school nurses, school-based health centers, parents, 

students, and others in the school community who 

are concerned about traffic-related air pollution 

exposure due to a school’s proximity to a heavily 

traveled roadway or trucking corridor and who 

want to understand potential approaches to 

reduce exposures. Other audiences that may find 

this resource applicable to their work include 

community-based environmental and health 

organizations; HVAC professionals, architects, 

design engineers, and construction contractors who 

can apply the principles of this document during 

facility siting, design, and construction; and other 

federal, state, local, and tribal agencies.

Other EPA Resources for 

Schools

The EPA website (www.epa.gov/schools) offers many 

documents and tools to help states, districts, schools, 

teachers, parents, and students create or enhance 

productive and healthy learning environments. 

These resources address a broad range of issues that 

affect children's health in schools, from selecting 

appropriate locations for schools to maintaining the 

buildings and grounds. Some of these resources 

may address strategies that are discussed in this 

publication. You can use these comprehensive 

resources to assess your school's environmental 

health efforts and implement or improve related 

programs, policies, and procedures. If you have 

questions about EPA’s resources for schools, contact 

your regional school coordinator.

1
Reducing Near-Road Pollution 

Exposure at Schools

Exposure to traffic-related air pollution has been linked 

to a variety of short- and long-term health effects, 

including asthma, reduced lung function, impaired 

lung development in children, and cardiovascular 

effects in adults. Children’s exposure to traffic-related 

air pollution while at school is a growing concern 

because many schools are located near heavily traveled 

roadways. This document briefly introduces the health 

risks associated with traffic-related pollution exposure 

and offers strategies to reduce students’ exposure in 

new and existing schools.

Near-Road Air Pollution and 

Children’s Health

Pollutants directly emitted from cars, trucks, and other 

motor vehicles are found in higher concentrations 

near major roads. Examples of directly emitted 

pollutants include particulate matter (PM), carbon 

monoxide, oxides of nitrogen, and benzene, though 

hundreds of chemicals are emitted by motor vehicles. 

Motor vehicles also emit compounds that lead to 

the formation of other pollutants in the atmosphere, 

such as nitrogen dioxide, which is found in elevated 

concentrations near major roads, and ozone, which 

forms further downwind. Beyond vehicles’ tailpipe and 

evaporative emissions, roadway traffic also emits brake 

and tire debris and can throw road dust into the air. 

Individually and in combination, many of the pollutants 

found near roadways have been associated with 

adverse health effects.

Studies show that concentrations oftraffic-related air pollutants can be elevated 

inside classrooms, and that traffic is one of the 

most significant sources of air pollution in both 

the indoor and outdoor school environments.

Motor vehicle pollutant concentrations tend to be 

higher closer to the road, with the highest levels 

generally within the first 500 feet (about 150 meters) 

of a roadway and reaching background levels within 

approximately 2,000 feet (about 600 meters) of a 

roadway, depending on the pollutant, time of day, and 

surrounding terrain.1

 Many scientific studies have found 

that people who live, work, or attend school near 

major roads appear to be more at risk for a variety of 

short- and long-term health effects, including asthma, 

reduced lung function, impaired lung development in 

children, and cardiovascular effects in adults. 

Children are particularly susceptible to health 

problems resulting from air pollution exposure due to:

• Respiratory systems that are not fully

developed. Studies show exposures to air

pollution in childhood can result in decreased

lung function.2

• Higher rates of exposure than adults because they

are more active and they breathe more rapidly.

Children spend a lot of time at school, and nearly 

17,000 schools in rural and urban areas across the 

U.S. are located within 250 meters (~820 feet) of a 

heavily traveled road.3 Exposure to traffic-related 

pollution is a concern both indoors and outdoors―

1 Karner, A. A., Eisinger, D. S., & Niemeier, D. A. (2010). Near-roadway air quality: Synthesizing the findings from real-world data. Environmental Science & Technology, 44(14), 5334-5344. 

doi:10.1021/es100008x 

2 Health Effects Institute. (2010). Traffic-related air pollution: A critical review of the literature on emissions, exposure, and health effects. Special Report 17. Available at http://pubs.

healtheffects.org/view.php?id=334

3 Kingsley, S. L., Eliot, M. N., Carlson, L., Finn, J., MacIntosh, D. L., & Suh, H. H. (2014). Proximity of US schools to major roadways: A nationwide assessment. Journal of Exposure Science and 

Environmental Epidemiology, 24, 253–259. doi:10.1038/jes.2014.5. This study defines major roadways as those with a Census Feature Class Code classification of A1 (primary road with 

limited access or interstate highway) or A2 (primary road without limited access).

2
3

concentrations tend to be higher outdoors, yet 

numerous studies have found that concentrations of 

traffic-related pollutants can also be elevated inside 

classrooms, where children spend most of the school 

day.4,5 In addition, diesel-powered school buses can 

be a significant source of pollution near schools. 

How Can Near-Road Pollution 

Exposure Be Reduced in 

Schools?

Over the past several decades, emission control 

technologies and regulations have led to large 

decreases in emissions per vehicle. Pollutant 

concentrations have also declined, though at a 

slower rate, because there has been growth in both 

the number of vehicles and vehicle miles traveled. 

Government and industry are still working to reduce 

the amount of pollutants emitted by motor vehicles. 

In the meantime, several strategies are being used 

by communities and schools across the country to 

reduce traffic-related pollution exposure. Some of 

these strategies aim to reduce indoor exposure at 

the individual building level, while others target 

reductions indoors and outdoors on a larger scale. 

Given the importance of PM in general, and diesel 

PM specifically as a harmful pollutant, the focus of 

this document is on strategies that can be used to 

mitigate PM exposure, although some techniques 

may be applicable to gaseous pollutants (e.g., 

carbon monoxide, benzene) as well. This document 

addresses the following mitigation strategies that 

can be implemented by local school authorities: 

ventilation, filtration, actions for building occupants, 

transportation policies, site location and design, and 

the use of roadside barriers. Many of these strategies 

may also be effective at reducing exposure at schools 

near other sources of particulate air pollution (e.g., 

railyards, industry) and near facilities that have 

increased truck and car traffic (e.g., warehouses, ports). 

In planning, implementing, and evaluating mitigation 

strategies, it may be valuable to assemble a diverse 

project team that is committed to ensuring a healthy 

environment for children and staff.6

Elevated PM concentrations

in schools have been linked to:

• Poor ventilation;

• Ineffective or nonexistent air filtration;

• Proximity to roadways;

• Open windows and doors allowing entry of

polluted outdoor air during rush hours;

• Infrequent and incomplete cleaning of indoor

surfaces; and

• High occupancy levels.7,8

Building Design and 

Operation Strategies for 

Reducing Near-Road 

Pollution Exposure

Ventilation, Filtration, and Indoor 

Air Quality in Schools

Proper building ventilation is crucial for maintaining 

healthy indoor air quality. Ventilation in schools is 

achieved passively (e.g., via open windows and doors) 

or mechanically by a building’s heating, ventilating, 

and air conditioning (HVAC) system.

4 Mejia, J. F., Choy, S. L., Mengersen, K., & Morawska, L. (2011). Methodology for assessing exposure and impacts of air pollutants in school children: Data collection, analysis and health 

effects - A literature review. Atmospheric Environment, 45(4), 813-823. doi:10.1016/j.atmosenv.2010.11.009

5 Mullen, N. A., Bhangar, S., Hering, S. V., Kreisberg, N. M., & Nazaroff, W. W. (2011). Ultrafine particle concentrations and exposures in six elementary school classrooms in northern 

California. Indoor Air, 21(1), 77-87. doi:10.1111/j.1600-0668.2010.00690.x

6 For more information on developing a project team, see EPA’s Energy Savings Plus Health guidelines (Appendix A). U.S. Environmental Protection Agency. (2014). Energy savings plus 

health: Indoor air quality guidelines for school building upgrades. Available at http://www.epa.gov/iaq/schools/pdfs/Energy_Savings_Plus_Health_Guideline.pdf

7 Stranger, M., Potgieter-Vermaak, S. S., & Van Grieken, R. (2008). Characterization of indoor air quality in primary schools in Antwerp, Belgium. Indoor Air, 18(6), 454-463.

8 McCarthy, M. C., Ludwig, J. F., Brown, S. G., Vaughn, D. L., & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. doi:10.1111/

ina.12015
4

Studies have shown that in addition to reducing 

health effects related to air pollution exposure, 

proper ventilation contributes to a comfortable 

learning environment associated with better test 

scores and attendance.9

However, improved ventilation does not always 

improve air quality. For example, if filtration is not 

used, higher ventilation rates can increase pollutant 

levels indoors if outdoor pollutant concentrations are 

higher than indoor concentrations.

Passive/Natural Ventilation

In passive or natural ventilation systems, air is supplied 

to a classroom through open windows or doors or 

by leaks in the building envelope (e.g., gaps around 

windows and doors). Passive systems rely on dilution 

of indoor air contaminants by mixing indoor air 

with outdoor air. This approach is only effective if 

the outdoor air is less polluted than the indoor air. 

It is often challenging to achieve proper ventilation 

using passive methods because assessing ventilation 

needs and outdoor air quality, as well as controlling 

ventilation rates, can be difficult for building occupants 

to carry out. Strategies for reducing pollution exposure 

in naturally ventilated classrooms include reducing 

indoor sources of air pollution and, at schools near 

heavily traveled roads, timing air intake (i.e., opening 

and closing doors and windows) to avoid bringing in 

outdoor air during peak travel times (see Actions for 

Building Occupants section for more information). 

Additionally, there are filtration-related options for 

schools with passive systems, which are described in 

the sections that follow.

Recommendations

• Keep windows and doors closed during peak

traffic times (e.g., morning and evening rush

hours).

• Minimize indoor sources of air pollution.

• Use a stand-alone filtration unit or upgrade to

a mechanical ventilation system.

Mechanical Ventilation

In mechanical ventilation systems, air is circulated 

through a building by air intake and/or exhaust 

fans. Mechanical systems used in schools can be 

grouped into two categories: units that serve a single 

room without air ducts (such as a unit ventilator 

or individual heat pump) and central air handling 

units that serve multiple rooms via ductwork. The 

effectiveness of mechanical ventilation depends 

on HVAC system type, design, maintenance, and 

operation. An imbalance in a building’s HVAC system 

can result in the building becoming pressurized. 

Negative pressure can allow outdoor contaminants 

to enter the building through the building envelope, 

while positive pressure prevents infiltration of 

outdoor air but can force moisture into the walls 

of the building. In cold climates, moisture can 

condense in walls and promote mold growth. 

Therefore, pressure relief dampers that allow air to 

exit the building or exhaust fans that draw air out are 

typically recommended.

The U.S. Environmental Protection Agency (EPA) 

recommends10 that central HVAC air handling units 

be used when possible, as they are often quieter (and 

therefore less likely to be turned off), easier to maintain 

because of the reduced number of individual units, and 

compatible with higher efficiency filtration.

While central units typically achieve higher air 

exchange rates and therefore better indoor air 

9 Mendell, M. J., & Heath, G. A. (2005). Do indoor pollutants and thermal conditions in schools influence student performance? A critical review of the literature. Indoor Air, 15(1), 27-52.

10 U.S. Environmental Protection Agency. (2012). Heating, ventilation and air-conditioning (HVAC) systems. Available at www.epa.gov/iaq/schooldesign/hvac.html
5

quality, the necessary ducting and registers tend to 

increase system cost. Ductwork in central ventilation 

systems should be kept clean and tested regularly 

for leaks. Regardless of the type of system used, 

mechanical ventilation systems are typically more 

reliable than natural methods because airflow rates 

are controllable. 

Recommendations

• Use mechanical ventilation if possible. Central HVAC

units that serve multiple classrooms are typically

more effective than single-room unit systems.

• In classrooms where sufficient mechanical

ventilation can be ensured, seal the building

envelope to prevent infiltration of polluted air

through cracks around windows, doors, and

HVAC ducts.

• With a properly performing mechanical

ventilation system, keep windows and

doors closed to avoid bringing in polluted

outdoor air.

• Ensure that HVAC systems are properly

maintained and operated.

• Locate air intakes away from roadways, bus idling,

drop-off zones, and other pollutant sources, such

as designated smoking areas.11

Filtration

Although diluting air contaminants through ventilation is 

sometimes adequate, many buildings (including schools) 

require additional air treatment to achieve suitable 

indoor air quality. Studies have shown that filtration 

in schools can improve indoor air quality by reducing 

particle concentrations by as much as 97% relative to 

outdoor levels.12 Achieving maximum performance of 

filtration systems requires:

• Proper installation;

• Continuous operation;

• A tight building envelope (i.e., minimal air leaks);

• Effective air distribution;

• Careful placement of air inlet and outlet

locations; and

• Regular maintenance, including replacement

of filters.

Filtration has some practical limitations. Filtration is 

only effective at removing particles that enter the 

system through an outside air intake and particles 

that enter through the return air ducts usually 

located at ceiling level. Particles entering the school 

through other pathways may not be removed (for 

instance, particles entering the classroom through 

open doors or windows, through leakage in the 

building envelope, from indoor sources, or from 

re-suspension from floors). In addition, removal 

of gaseous pollutants by filtration is typically less 

effective than particle removal; filters that are able 

to remove gaseous pollutants are costly and are not 

commonly used in schools.

Indoor air filtration is typically incorporated into a 

building’s HVAC system, although portable, standalone air cleaners are also available. Both system 

types typically employ filters that remove air 

contaminants based on particle size.13

Schools undertaking energy

efficiency upgrade projects may wish to 

consider concurrent opportunities to improve 

indoor air quality.14

11 The Centers for Disease Control and Prevention recommends that schools prohibit all tobacco use at all school facilities and events at all times. See http://www.cdc.gov/healthyschools/

tobacco for more recommendations on tobacco use prevention through schools.

12 McCarthy, M. C., Ludwig, J. F., Brown, S. G., Vaughn, D. L., & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. doi:10.1111/

ina.12015

13 Some portable, stand-alone air cleaners use alternate technologies to remove contaminants, such as electrostatic precipitators. While effective at removing particles, electrostatic 

precipitators tend to be more expensive than traditional filters, require more maintenance over time, and can generate small amounts of ozone as a by-product of air purification. In 

addition, some air cleaners are designed to intentionally generate ozone and are not recommended. The California Air Resources Board maintains a list of air cleaning devices tested and 

certified by the State of California to meet California’s electrical safety and ozone emission requirements. See http://www.arb.ca.gov/research/indoor/aircleaners/certified.htm

14 U.S. Environmental Protection Agency. (2014). Energy savings plus health: Indoor air quality guidelines for school building upgrades. Available at http://www.epa.gov/iaq/schools/energy_

savings_plus_health.html
6

The degree of indoor air quality improvement from 

filtration depends on the filter’s Minimum Efficiency 

Reporting Value (MERV) rating. Filters with MERV 

ratings from 1 to 4 are effective at removing large 

particles (e.g., pollen, dust mites, paint dust), but 

are less effective at removing small, traffic-related 

particles that can enter the respiratory system and 

cause adverse health effects. Filters with higher MERV 

ratings are increasingly more effective at removing 

very small particles.

Studies examining filtration systems in schools have 

found that all types of filtration systems improve 

air quality conditions inside classrooms and can be 

used to reduce exposure to traffic-related pollutants 

indoors. Central HVAC systems equipped with 

filters tend to be more effective than unit systems 

(e.g., window units) with filters. In schools with 

central HVAC systems, medium-efficiency filters 

(MERV 6–7) tend to reduce particle concentrations 

by approximately 20% to 65%, while higher 

performance filters (MERV 11–16) can reduce particle 

concentrations from 74% to 97% relative to outdoor 

concentrations.15 Higher MERV ratings are generally 

associated with higher particle removal rates. Standalone systems, although slightly less effective, are 

well-suited for classrooms that are not equipped 

with a central HVAC system and can achieve removal 

I

n a pilot study of highperformance filtration in schools,

the South Coast Air Quality Management 

District found that the combined use of 

register-based and high-performance panel 

filters was most effective at reducing particle 

concentrations, with reductions of 87–96%, 

while the use of the high-performance panel 

filter alone reduced particle concentrations 

by close to 90%.16

efficiencies close to 90%.17 However, performance 

depends on the amount of air that can be processed 

by the unit and other classroom layout features 

that influence airflow to the system. A downside of 

some stand-alone units is that they can be noisier 

than HVAC-based filtration. However, quieter standalone units are available that meet the noise level 

requirements for new classroom equipment.18

It is important to maintain HVAC filtration 

performance through regular maintenance 

and proper HVAC system operation. Excessive 

depressurization can be avoided by routine cleaning 

and filter replacement as necessary. Monitoring 

the system pressure can help identify when 

filter replacement is needed and can maximize 

performance, minimize energy costs, and prevent 

early disposal of useful filters. Inexpensive pre-filters 

can be used to remove a majority of particle mass 

and extend the life of the more expensive main filter. 

Filter performance and lifetime can also be improved 

by locating outdoor air intakes away from potential 

pollution sources so that cleaner air is drawn into 

the system.

Some schools may be able to incorporate highefficiency filtration into their existing HVAC system. 

However, not all HVAC systems are compatible 

with high MERV-rated filters. In some systems, the 

addition of a high MERV-rated filter can result in 

15 McCarthy, M. C., Ludwig, J. F., Brown, S. G., Vaughn, D. L., & Roberts, P. T. (2013). Filtration effectiveness of HVAC systems at near-roadway schools. Indoor Air, 23(3), 196-207. doi:10.1111/

ina.12015

16 Polidori, A., Fine, P. M., White, V., & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013 

17 Polidori, A., Fine, P. M., White, V., & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013 

18 Polidori, A., Fine, P. M., White, V., & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013 
7

a large drop in system pressure. The magnitude 

of the pressure drop varies by filter type and not 

all high-efficiency filters result in a large drop in 

pressure. For example, the South Coast Air Quality 

Management District’s school air filtration program 

uses high-performance panel filters that have air 

resistance properties similar to conventional filters, 

do not require the use of a pre-filter, and do not 

reduce airflow through the HVAC system. In addition, 

these filters have longer lifespans than the mediumefficiency MERV filters typically in use, requiring 

replacement approximately once per year rather than 

every four months.19 Depending on the HVAC system, 

installing the highest MERV-rated filter that the 

current system can handle may be a cost-effective 

way to improve indoor air quality. In other cases, 

improving or replacing the existing HVAC system 

may be required to achieve the pumping capacity 

necessary to accommodate high-efficiency filtration 

because of limited airflow. 

Capital and/or increased operating costs may pose 

limitations to these improvements; however, potential 

savings associated with any system upgrades should 

also be considered. For example, the cost of purchasing 

an air sensor to monitor ventilation needs, and thereby 

help optimize ventilation rates, could offset long-term, 

higher energy costs due to over-ventilation.

Recommendations

• For classrooms relying on passive/natural

ventilation, use quiet, portable, standalone filtration systems to reduce indoor

concentrations.

• For schools with mechanical ventilation

systems, use high-efficiency filtration to

reduce particle pollution exposure inside

classrooms.

• Upgrade filtration to the highest MERV-rated

filters that the HVAC system can handle.

• Consider HVAC system upgrades to

accommodate high-efficiency filtration, including

the installation of pre-filters, if necessary.

• Inspect and replace filters regularly according

to manufacturer recommendations.

• Where possible, locate air intakes away from

pollution sources.

Actions for Building Occupants

The actions of building occupants can greatly affect 

near-road pollution exposure indoors. For instance, 

opening windows or doors for ventilation in classrooms 

can allow polluted air to enter into the classroom 

and overwhelm the air quality benefits of an HVAC 

filtration system. Keeping windows and doors closed 

is especially important during periods of peak traffic 

(e.g., morning and evening rush hours) when near-road 

pollutant concentrations are typically highest. Although 

the classroom is a noise-sensitive environment, it 

is important that HVAC systems are not turned off 

during the day.

For naturally ventilated classrooms, there may be 

opportunities to time air intake to avoid bringing in 

outdoor air during peak concentration times.

Although the focus of this document is traffic-related 

pollution exposure, it is important to note that indoor 

sources can largely impact (or even dominate) indoor 

concentrations of PM and gaseous pollutants. Indoor 

19 Polidori, A., Fine, P. M., White, V., & Kwon, P. S. (2013). Pilot study of high-performance air filtration for classroom applications. Indoor Air, 23(3), 185-195. doi:10.1111/ina.12013
8

sources include combustion sources, secondhand 

smoke, dust from student activity (PM), and (gaseous) 

emissions, such as from building materials, furniture, 

carpets, air fresheners, personal care products, 

biologically derived emissions from mold and bacteria, 

and classroom supplies (e.g., dry erase markers and 

some cleaners).

Exposure outdoors may be reduced by carefully timing 

outdoor activities to avoid times of peak pollution. 

Ozone pollution is often worse on hot, sunny days, 

especially during the afternoon and early evening. 

Particle pollution can be high any time of day, but higher 

levels can be found near idling cars, trucks, and buses 

and near busy roads, especially during rush hour. If 

possible, plan strenuous outdoor activities outside of 

rush hour and drop-off/pick-up times, and consider 

locating activities farther from roads and loading zones. 

In addition, many schools implement the Air Quality 

Flag program to raise awareness of the daily air quality 

forecast. The school flags, combined with information 

on current air quality from www.airnow.gov, can be 

used to help plan outdoor activities.

Raising awareness about indoor and outdoor air quality 

issues and providing training for staff on optimal 

building operating practices (including HVAC operation) 

specific to the design of their school are inexpensive 

strategies that can supplement upgrades to the 

ventilation and filtration system and building and site 

design. EPA’s IAQ Tools for Schools program provides 

an easy-to-use framework and set of tools to train 

staff on indoor air quality (IAQ) management (www.

epa.gov/iaq/schools). Training is recommended as a 

complementary strategy and should not be considered 

an alternative to ventilation upgrades.

Recommendations

Train teachers and school staff on best ventilation 

practices, including: 

• Keeping windows and doors closed in

mechanically ventilated classrooms to prevent

entry of polluted outdoor air.

• Keeping windows and doors closed in

naturally ventilated classrooms during peak

commute times.

• Keeping HVAC systems turned on throughout

the day.

• Keeping air vents clear of items that may

block airflow.

• Understanding the importance of indoor

pollutant sources and how to reduce

emissions from indoor sources.

Plan strenuous outdoor activities during times 

with lower amounts of traffic.

Summary

Ventilation and filtration needs vary by school 

according to occupancy, proximity to roadways or 

other pollutant sources, and the prevalence of indoor 

sources. School administrators can improve indoor air 

quality by modifying ventilation and filtration systems, 

yet it can be difficult to identify which strategies will 

yield the most significant improvements for the level 

of effort and cost required.

To evaluate which (if any) actions may be needed 

to help reduce exposure to traffic-related pollution, 

school staff can begin by making a preliminary 

assessment. A brief guide to assist in the assessment 

of a school ventilation and filtration system is 

provided on page 15. Once a baseline assessment of 

the current ventilation system is complete, mitigation 

strategies suitable for the system can be evaluated. 

Table 1 offers mitigation strategies for different types 

of ventilation systems typically found in classrooms. 
9

Table 1. Ventilation systems versus mitigation strategies. HVAC/ventilation system types are listed from 

generally less effective to more effective, and mitigation strategies are listed from the simplest (and least 

costly) to implement to those that require a higher level of effort.

Site-Related Strategies for 

Reducing Near-Road Pollution 

Exposure

Transportation Policies

Establish Anti-Idling and Idle Reduction Policies

Bus operation and idling can produce large amounts 

of PM and other air pollutants. Some schools have 

instituted anti-idling or idle reduction policies 

to reduce the impact of pollution from buses 

and passenger vehicles near schools. Anti-idling 

policies can result in large decreases in particle 

concentrations, particularly at schools operating 

multiple diesel school buses.

HVAC/Ventilation 

Type

Mitigation Strategies

Educate 

Staff Air-Seal Building Improve Air Intake Use Filtration Upgrade System

Passive/natural 

ventilation

May be an option if 

adequate ventilation 

to dilute and 

remove pollutants 

from indoor sources

Avoid bringing in air 

during periods of high 

traffic

Use a portable 

stand-alone 

filtration system

Switch to a 

mechanical 

ventilation method

Single-classroom 

HVAC unit (e.g., 

window unit)

Avoid airflow 

obstructions

Use quiet systems

Use highest 

compatible 

MERV-rated filter

Use pre-filters or 

high-performance 

panel filters

Upgrade to a 

central HVAC 

system

Central HVAC system 

serving multiple 

classrooms—highefficiency filtration 

use limited by airflow

Change air intake 

locations if near 

pollution source(s) 

(e.g., roadway, drop-off 

zone, parking)

Use highest 

compatible 

MERV-rated filter

Use pre-filters or 

high-performance 

panel filters

Modify airflow to 

be compatible with 

higher efficiency 

filtration

Central HVAC system 

serving multiple 

classrooms—highefficiency filtration 

use not limited by 

airflow

Change air intake 

locations if near 

pollution source(s) 

(e.g., roadway, drop-off 

zone, parking)

Use MERV 16+ 

filter

Use pre-filters

N/A

Upgrade Bus Fleets

Pollution from school buses can also be reduced by 

upgrading bus fleets. Fleet turnover for diesel school 

buses is low, with buses typically operating for 20 to 30 

years. Older buses emit high levels of PM and other air 

pollutants. However, technological advances and tighter 

PM emissions standards for new buses, set by EPA, have 

resulted in new buses (manufactured during or after 

2007) that are 60 times cleaner than buses produced 

prior to 1990.Emissions can be reduced by retrofitting 

older school buses with PM filters or oxidation catalysts, 

or by replacing older buses with newer models. 

Emissions may be reduced by using certain alternative 

fuels, including biodiesel blends. Engines certified to 

operate on alternative fuels such as liquid petroleum 

gas (LPG), compressed natural gas (CNG), and liquefied 

natural gas (LNG) can also reduce emissions. Discuss 

potential funding options for bus fleet upgrades with 

your state or local environmental or air quality agency.20

20 U.S. Environmental Protection Agency. (2010). Clean school bus. Available at http://www.epa.gov/cleandiesel/sector-programs/csb-overview.htm
10

Encourage Active Transportation

Promoting active transportation, such as walking and 

bicycling to and from schools, can help reduce trafficrelated pollution by reducing the number of buses 

and passenger vehicles nearby. For example, the 

addition of walking/biking paths at Roosevelt Middle 

School in Eugene, Oregon, reduced traffic volumes 

near the school by 24%.21

While active transportation may contribute to 

improved air quality near schools, students walking 

or biking to school may be exposed to roadway 

pollution and other traffic hazards because of 

their proximity to motor vehicle traffic. When safe 

alternatives exist, biking and walking to school along 

routes with lower traffic volumes may help reduce 

exposure to pollution and safety hazards.22

Parallel and off-street walking/biking paths through 

parks or other off-road areas can also provide a 

good alternative to traveling along a road with many 

motor vehicles. Pursuing pedestrian and bicycle 

infrastructure improvements can help provide safer 

routes for students to walk and bike to school. This 

could include installing or improving sidewalks, 

crosswalks, signs, markings, and countdown timers, 

as well as encouraging “walking” school buses.23

When considering walking and biking routes to 

school, impacts on safety, lighting, access, and 

maintenance requirements should be considered. The 

Safe Routes to School National Partnership provides 

many resources on promoting safe walking and 

biking (www.saferoutespartnership.org).

Despite the potential for increased exposure 

associated with active transportation, walking and 

biking have been shown to improve health, and 

people who live in highly walkable neighborhoods 

are generally more physically active than those who 

live in less walkable neighborhoods. Promoting 

walking and biking to school along routes or paths 

with lower traffic volumes (relative to other roads) 

will increase the likelihood that the health benefits 

of exercise outweigh the health risks associated with 

increased air pollutant exposures.

Recommendations

• Limit school bus idling by instituting antiidling or idle reduction policies.

• Upgrade school bus fleets by:

– Retrofitting buses with PM filters or

oxidation catalysts; and

– Replacing older buses with newer models.

• Emissions may be reduced by using certain

alternative fuels, including biodiesel blends.

Engines certified to operate on alternative fuel

such as LPG, CNG, and LNG can also reduce

emissions.

• Discuss funding opportunities for bus

fleet upgrades with your local or state

environmental or air quality agency.

• Provide walking and biking paths to promote

active transportation and reduce the number of

buses and passenger vehicles near the school.

Site Location and Design

In response to concerns about the impacts of near-road 

air pollution, several agencies, including EPA 

and several state agencies in California, have established 

siting guidelines for new schools that recommend 

reducing traffic-related air pollution exposure (Table 2). 

While California guidelines recommend that new schools 

should not be located within 500 feet or more of major 

roads, EPA’s School Siting Guidelines note the need to 

consider multiple issues associated with exposure and 

health. For example, a school sited far from a major road 

21 Safe Routes to School National Partnership. (2012). Safe routes to school and traffic pollution: Get children moving and reduce exposure to unhealthy air.

Available at http://www.saferoutespartnership.org/sites/default/files/pdf/Air_Source_Guide_web.pdf

22 Safe Routes to School National Partnership. (2012). Safe routes to school and traffic pollution: Get children moving and reduce exposure to unhealthy air.

Available at http://www.saferoutespartnership.org/sites/default/files/pdf/Air_Source_Guide_web.pdf

23 National Center for Safe Routes to School. (2013). Starting a walking school bus. Available at http://www.walkingschoolbus.org
11

that requires long commutes by bus or car may result 

in higher overall exposure for students, compared to 

a school site near a major road that does not require 

long commutes. Overall, EPA recommends multiple 

strategies, as described in this document, to reduce 

students’ overall exposure.

School sites include of a variety of land use types, 

such as classrooms, playgrounds, athletic fields, 

offices, and maintenance and storage facilities. For 

new school developments near roadways, there 

may be opportunities to reduce traffic-related 

pollution exposure through careful site design. By 

Table 2. School siting documents developed by various agencies.

Agency Guidance Key Outcomes

U.S. EPA School Siting 

Guidelines (2011)

Recommends considering many factors in evaluating locations for new schools, 

including proximity to the community (including community amenities and 

infrastructure), distance from major transportation facilities, exposure to air 

pollutants during student commutes, feasible mitigation on site, and accessibility by 

walking or biking.

California Air 

Resources Board

Air Quality and 

Land Use Handbook 

(2005)

Recommends that new schools are not located within 500 feet of major roadways 

(>50,000 vehicles/day).

California 

Department of 

Education

School Site Selection 

and Approval Guide 

(2000)

Recommends distancing schools 2,500 feet from major roadways where explosives 

are carried and at least 1,500 feet from roads where gasoline, diesel, propane, 

chlorine, oxygen, pesticides, or other combustible or poisonous gases are 

transported.

South Coast 

Air Quality 

Management 

District

Air Quality Issues 

in School Site 

Selection: Guidance 

Document (2005, 

updated 2007)

Recommends a buffer zone of no less than 500 feet, and as much as 1,000 feet, 

between schools and major roadways.

Los Angeles 

Unified School 

District

Distance Criteria for 

School Siting (2008)

Recommends that new schools are not built within 500 feet of a freeway or major 

transportation corridor (>100,000 vehicles/day).

Sample layouts for a large land parcel with a school and other land uses. A less desirable layout (left) with the school located close to 

the highway is compared to an improved layout (right) with the school more than 500 feet from the highway (red dotted line).
12

locating land uses such as maintenance, storage, 

parking, and office facilities in the area closest to the 

roadway, classroom and play areas can be located 

farther from the roadway in areas where air pollutant 

concentrations tend to be lower. Some of these 

strategies may also be applicable to existing school 

sites near roadways, or to sites located near other 

sources of diesel particulate air pollution such as 

warehouses, truck routes, railyards, and ports.

Exposure to traffic-related pollution can also be 

reduced by locating onsite transportation-related 

sources, especially school bus drop-off and pick-up 

locations, as far from classrooms, play areas, and 

building air intakes as possible. Optimal placement of 

offices, playgrounds, athletic fields, and classrooms 

within a school site depend on a variety of factors, 

including typical wind patterns, the amount of time 

spent and activities performed outdoors versus 

indoors, and indoor ventilation conditions.

Recommendations

• For new school developments, consider

locations farther from major roads and other

areas with heavy truck traffic, but still within

the community.

– A quantified evaluation of post-mitigation

air quality impacts may be appropriate 

and/or required.

• Consider unintended consequences of

any location, such as increased commute

distances and decreased opportunity for

walking and biking.

• Consider opportunities to locate playgrounds,

athletic fields, and classrooms farther from

the roadway, or other areas with heavy truck

traffic, by locating maintenance, storage,

parking, and office facilities in the area closest

to the roadway.

• Locate bus and passenger vehicle loading

zones away from classrooms, play areas, and

building air intakes.

Roadside Barriers

Sound Walls

Pollutant concentrations behind a barrier located 

downwind of a roadway are typically lower than 

concentrations in the absence of a barrier. Studies 

show that reductions in downwind pollutant 

concentrations within approximately 500 feet of a 

highway in the presence of a well-designed sound 

wall can be on the order of 15% to 50%.24

The effectiveness of sound walls at mitigating 

near-road pollution exposure depends on roadway 

configuration, local meteorology, and barrier height, 

design, and endpoint location. For example, pollutant 

concentrations may be higher downwind of a wall 

if there are gaps in the wall that allow pollutants to 

pass through. Sound walls can be considered for 

schools located adjacent to highways and other busy, 

high-traffic roadways.

I

n situations where school authorities

do not have jurisdiction or ownership 

over the immediate roadside environment, 

consider discussing the use of roadside 

barriers to reduce traffic-related pollution 

exposure with the relevant authority (e.g., 

state department of transportation, city 

planning department).

24 Baldauf, R. W., Khlystov, A., Isakov, V., Thoma, E., Bowker, G. E., Long, T., & Snow, R. (2008). Impacts of noise barriers on near-road air quality. Atmospheric Environment, 42, 7502–7507.
13

The combined use of vegetation

and sound walls has shown promise in 

reducing vehicle pollution downwind of 

roadways by up to 60%.25

Vegetation

Trees and plants along roadways can reduce 

particle concentrations by acting as a physical 

barrier between roadways and schools (similar, in 

effect, to sound walls), or by filtering particles as 

they pass through and accumulate on leaf surfaces. 

The amount of removal depends on season, plant 

species, leaf size and density, and pollutant type. 

The effectiveness of trees and plants as physical 

barriers also depends on the density and height of 

the greenery. Mature vegetation tends to be more 

effective than young vegetation, evergreen species 

are typically more effective than deciduous species, 

and vegetation with needle-like greenery (e.g., 

conifers) tends to be more effective than broadleaved trees. Particle removal rates tend to be higher 

when vegetation is located close to the pollutant 

source and when wind speeds are low.

The vegetation types chosen for roadside barriers 

should be appropriate for the location of interest, 

including water requirements, non-invasive species, 

and aesthetics. In general, the vegetation barrier should 

be thick (approximately 20 feet or more) and have full 

leaf and branch coverage from the ground to the top 

of the canopy along the entire length (i.e., no gaps 

in-between or underneath the vegetation). In some 

instances, this type of barrier may require the use of 

multiple vegetation types such as a combination of 

bushes and trees. The vegetation chosen should also 

maintain its structure during all seasons; thus, coniferous 

trees would be preferable to hardwood species. The 

vegetation types chosen should also not be emitters of 

air pollution or high levels of pollen. Schools can use the 

U.S. Department of Agriculture’s (USDA’s) i-Tree Species 

tool26 to begin the process of choosing appropriate 

vegetation, in consultation with other experts from plant 

nurseries, local cooperative extensions, city government, 

or the U.S. Forest Service. All vegetation that will be 

located near a road should be sited consistent with state 

and local safety guidelines. 

Recommendations

• Use a solid roadside barrier (only along

highways) and/or vegetation to block trafficrelated pollutants from influencing air quality

near the school.

• Minimize gaps in solid and vegetative

roadside barriers.

• For vegetative barriers, use an evergreen

species with mature, dense greenery and

locate the barrier downwind and close to the

roadway.

• Choose species appropriate for region and

site, consulting with plant nurseries, local

cooperative extensions, city governments, or

the U.S. Forest Service.

Similar to sound walls, concentrations may be higher 

behind a vegetative barrier that is located downwind of 

the roadway if there are gaps in the vegetation such as 

missing or dead trees, or lack of cover from the ground 

to the top of the vegetation. In any case, vegetation can 

be used as a buffer to distance people from the roadway 

while creating a more attractive and shaded space that 

encourages active transportation (such as walking and 

bicycling) as an alternative to vehicle use.27

25 Bowker, G. E., Baldauf, R., Isakov, V., Khylstov, A., & Petersen, W. (2007). The effects of roadside structures on the transport and dispersion of ultrafine particles from highways. 

Atmospheric Environment, 41, 8128-8139. 

26USDA’s i-Tree Species is designed to aid users in selecting proper species given the tree functions they desire. The tool is available at www.itreetools.org/species.

27 Baldauf, R., McPherson, G., Wheaton, L., Zhang, M., Cahill, T. Hemphill Fuller, C., Withycombe, E., & Titus, K. (2013). Integrating vegetation and green infrastructure into sustainable 

transportation planning. Transportation Research News, September-October, 14-18.
14

Summary of Recommendations

Table 3 outlines mitigation strategies that can be used to reduce traffic-related pollution exposure in schools, 

including ventilation/HVAC system requirements, benefits, drawbacks, and relevance for new and/or existing 

schools. Note that some of these mitigation strategies will only serve to reduce pollution exposures indoors 

(e.g., filtration), or will only effectively reduce some pollutants (e.g., PM2.5) but not others (e.g., volatile organic 

compoundss). These mitigation strategies reduce risks, but do not eliminate them.

Strategy

Ventilation/

HVAC System 

Type

Benefits Drawbacks

New/

Existing 

Schools

Educate staff on 

ventilation and 

indoor air quality 

best practices

All

Teachers are less likely to turn 

mechanical systems off; air vents 

remain unobstructed; doors/windows 

are kept closed during peak pollution 

periods; indoor sources of air pollution 

are reduced

Effectiveness may decrease over time; 

results depend on training quality and staff 

cooperation

Both

Air-seal around 

windows, doors, 

HVAC ducts, etc.

Mechanical 

ventilation 

systems

Reduces the amount of unfiltered air 

entering the building

Indoor pollutant concentrations may build 

over time if ventilation is insufficient, especially 

if indoor pollutant generation is high

Both

Relocate air 

intake or source if 

roadway/pollution 

source is near intake 

vent 

Central HVAC 

systems; 

single 

classroom 

HVAC units

Reduces particle and gaseous 

concentrations in incoming air; 

can increase lifespan of filters

Cost Both

Use filtration All Reduces particle concentrations from 

both outdoor and indoor sources

Maintenance and replacement required; may 

require system upgrades Both

Improve HVAC 

system design to 

be compatible with 

high-efficiency 

filtration

Central HVAC 

systems

Larger reductions in particle 

concentrations are possible Cost Both

Implement antiidling/idle reduction 

policies

All Reduces emissions of particles and 

gases 

Lack of vehicle climate control during hot/cold 

weather Both

Upgrade school bus 

fleet All Reduces emissions of particles and 

gases

Cost Both

Encourage active 

transportation (e.g., 

walking and biking) 

to school

All Reduces emissions of particles and 

gases; improved health with exercise

Walkers/bicyclists may be exposed to trafficrelated pollution or other hazards during trips Both

Locate school site 

away from pollution 

sources

All

May reduce student exposure to 

particles and gases at the school, 

although overall exposures may 

increase if an alternative site requires 

long commutes by bus or car

If alternative sites are limited, there may not 

be opportunities to locate the school farther 

from the road; unintended consequences from 

locating sites far from the community may 

include a decreased opportunity for walking 

and biking, increased traffic, and/or increased 

exposures during commuting

New

Design school site to 

minimize exposure 

to pollutant sources

All Reduces student exposure to particles 

and gases

Effectiveness is site-specific; may be costly for 

existing schools Both

Use solid and 

vegetative barriers All

Reduces concentrations of particles 

and gases near schools; vegetative 

barriers may increase shade and 

improve aesthetics

Cost; optimal design may be site-specific; 

maintenance and water needs for vegetative 

barriers

Both
15

School Ventilation and 

Filtration System Assessment

1. Assess whether near-road pollution may be a problem.

• Is there a major roadway near the school? If so:

– How far away is it?

– Is the school downwind of the road?

• Where does school bus pick-up and drop-off occur?

– Are there opportunities to reduce bus idling or relocate loading zones away from classrooms and

outdoor recreation areas?

2. Assess the current ventilation and filtration system.

• Is ventilation achieved passively or mechanically?

• If mechanical:

– Is a central HVAC system used or a single-classroom unit?

– Are filters being used?

– What is the blower capacity?

– Is filtration being used? If so, what is the MERV rating of the filter(s)?

3. Assess ventilation operation.

• Are teachers leaving windows and/or doors open during the day?

• Are there opportunities to bring in air during off-peak emission times?

• Are teachers turning systems off due to noise issues?

• Are filters being inspected, cleaned, and replaced according to the schedule recommended by the

manufacturer?

4. Assess air-sealing needs to limit infiltration of unconditioned air.

• Can infiltration of polluted air be reduced by sealing around any of the following:

– Windows?

– Doors?

– HVAC ducting?

5. Evaluate air intake location(s) relative to roadways or other pollutant sources such as school bus drop-off and

pick-up locations.

• Is air intake located near a roadway, loading zone, or other pollutant source, such as designated

smoking areas?28 Are supply and exhaust vents unobstructed?

• Can the air intake be relocated to an area that is less influenced by pollutant sources?

28 The Centers for Disease Control and Prevention recommends that schools prohibit all tobacco use at all school facilities and events at all times. See http://www.cdc.gov/healthyschools/

tobacco for more recommendations on tobacco use prevention through schools.
16

Additional Resources

Information regarding air quality and pollution mitigation in schools is available on the EPA website: 

• General information about indoor air quality: www.epa.gov/iaq

• Creating healthy indoor environments in schools: www.epa.gov/iaq/schools

• Energy Savings Plus Health: Indoor Air Quality Guidelines for School Building Upgrades:

www.epa.gov/iaq/schools/energy_savings_plus_health.html

• EPA School Siting Guidelines: www.epa.gov/schools/guidelinestools/siting/download.html

• Exhibit 5: Factors Influencing Exposures and Potential Risks: www.epa.gov/schools/guidelinestools/siting/

downloads/Exhibit_5_Factors_Infl encing_Exposures_and_Potential_Risks.pdf

• Exhibit 6: Screening Potential Environmental, Public Health and Safety Hazards: www.epa.gov/schools/

guidelinestools/siting/downloads/Exhibit_6_Screening_Potential_Environmental_Public_Health_and_

Safety_Hazards.pdf

• HVAC systems in schools: www.epa.gov/iaq/schooldesign/hvac.html

• EPA Clean School Bus Program: www.epa.gov/cleanschoolbus/csb-overview.htm

• The Role of Vegetation in Mitigating Air Quality Impacts from Traffic Emissions: http://archive.epa.gov/nrmrl/

archive-appcd/web/pdf/baldauf.pdf

• EPA School Flag Program: http://cfpub.epa.gov/airnow/index.cfm?action=fl g_program.index

Other useful resources include:

• California Air Resources Board, Air Quality and Land Use Handbook: www.arb.ca.gov/ch/handbook.pdf

• South Coast Air Quality Management District, Air Quality Issues in School Site Selection: Guidance

Document: www.aqmd.gov/docs/default-source/planning/air-quality-guidance/school_guidance.pdf

• South Coast Air Quality Management District, Near-Road Mitigation Measures and Technology Forum

Materials: www.aqmd.gov/home/library/technology-research/technology-forums

• California Department of Education, School Site Selection and Approval Guide:

www.cde.ca.gov/ls/fa/sf/schoolsiteguide.asp

• Los Angeles Unified School District, Distance Criteria for School Siting:

www.lausd-oehs.org/docs/Misc/DistanceCriteriaTable%20Rev12_10_08.pdf

• ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality, 2013:

www.techstreet.com/ashrae/products/1865968

• ASHRAE Indoor Air Quality Guide: Best Practices for Design, Construction, and Commissioning, 2009:

www.ashrae.org/resources--publications/bookstore/indoor-air-quality-guide
c
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November 2015

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