Support us

Air pollutionUnited States

An introduction to the traffic rules and road signs of United States. Learn about driving, road safety and much more in our illustrated book, with answers to frequently asked questions.

For informational purposes only. Always follow official regulations. Some content and images were created with AI assistance.

Traffic signs
Traffic rules
United States

92. Air pollution

Air pollution is the presence of gases, particles or other substances in the air at concentrations that can harm human health, the environment or ecosystems. Road traffic contributes to air pollution through exhaust emissions and through non-exhaust sources such as brake wear, tyre wear and road dust.

Important traffic-related pollutants include nitrogen oxides, particulate matter, carbon monoxide and volatile organic compounds. Some pollutants are emitted directly by vehicles, while others can form in the atmosphere through chemical reactions. Vehicle-emission standards, cleaner technologies and traffic-management measures are used to reduce these emissions.

Air pollution
Black smoke emitted from a vehicle exhaust on a road in Kamonyi District. (Rwanda)
Wikimedia.org • Emmanuelkwizera • CC BY-SA
What is air pollution?

Air pollution is the presence of harmful gases, particles or other contaminants in the air. Road transport can contribute through engine emissions, vehicle wear and dust; the sources and pollutants differ by vehicle and conditions.

🔗 epa.gov • US EPA, smog and vehicle emissions

🔗 epa.gov • US EPA, Particulate Matter Basics

🔗 fhwa.dot.gov • US FHWA, particulate matter and road-transport sources

🔗 epa.gov • US EPA, AP-42 section 13.2.1.1, paved-road emissions and dust resuspension

How does road traffic cause air pollution?

Vehicles with combustion engines can emit exhaust pollutants. Road traffic also produces particles through brake, tyre and road-surface wear and can stir up road dust. Vehicles without tailpipe emissions can still contribute to these non-exhaust sources.

🔗 epa.gov • US EPA, smog and vehicle emissions

🔗 epa.gov • US EPA, Particulate Matter Basics

🔗 fhwa.dot.gov • US FHWA, particulate matter and road-transport sources

🔗 epa.gov • US EPA, AP-42 section 13.2.1.1, paved-road emissions and dust resuspension

Which air pollutants are associated with road traffic?

Important traffic-related pollutants include nitrogen oxides, particulate matter, carbon monoxide and volatile organic compounds. Their relative importance depends on the vehicle, fuel and driving conditions.

🔗 epa.gov • US EPA, smog and vehicle emissions

🔗 epa.gov • US EPA, Particulate Matter Basics

🔗 fhwa.dot.gov • US FHWA, particulate matter and road-transport sources

🔗 epa.gov • US EPA, AP-42 section 13.2.1.1, paved-road emissions and dust resuspension

1 United States 2 Motorway 3 Expressway 4 Speed limit 5 Minimum speed 6 Advisory speed 7 Bike path 8 Pedestrian warning 9 Tunnel 10 Bridge 11 Speed bump 12 Toll road 13 One-way traffic 14 Slope 15 Bus lane 16 Bus stop 17 Dead end 18 Stop sign 19 Give way 20 Roundabout 21 Road narrowing 22 Pedestrian crossing 23 Railway crossing 24 Mandatory direction 25 Turn prohibition 26 School area 27 Crossing animals 28 Slippery road 29 Rockfall 30 Aircraft 31 Curve 32 Chevron 33 Wrong-way driving 34 Roadworks 35 Height limit 36 Weight limit 37 Radar speed sign 38 Selective barriers 39 Traffic lights 40 Traffic lights warning 41 Pedestrian lights 42 Road markings 43 Bike box 44 Speed feedback 45 Driving licence 46 Traffic mirror 47 Emergency telephone 48 Cycling route 49 Parking 50 No parking 51 No stopping 52 Parallel parking 53 Park and ride 54 Kiss and ride 55 Disabled parking 56 Traffic management 57 Reversing 58 U-turn 59 Carpool 60 Detour 61 Uncontrolled crossroad 62 Ramp 63 Exit 64 Horse riding 65 Emergency exit 66 Runaway truck ramp 67 Oversize load 68 City limit 69 Tourist attraction 70 Horn 71 Axle weight limit 72 Licence plate 73 Charging station 74 Flooding 75 Dip 76 Horse 77 Local traffic 78 Pedestrian 79 Cyclist 80 Motorcycle 81 Truck 82 Bus 83 Police 84 Ambulance 85 Police signals 86 Gravel road 87 Pothole 88 Median strip 89 Public property 90 Path 91 Particulates 92 Air pollution 93 Interchange 94 Rush hour 95 Filling station 96 Road code 97 Two-way traffic 98 Passing lane 99 Street gutter 100 Road debris ...