Related by context. Frequent words. (Click for all words.) 64 idling 44 Fuel Efficiency 43 Fuel Economy 42 Pollution 42 Emissions 41 Air Pollution 41 Littering 41 particulate emissions 40 Clean Fuels 40 Polluting 40 nitrogen oxide 40 exhaust emissions 40 Speed Limit 39 Clean Air 39 Speeding 39 Greenhouse Gas Emissions 39 Commute 39 Flaring 39 Derailment 38 Distracted Driving 38 snarls traffic 38 Biking 38 Driving 38 diesel 38 Commuting 38 Greenhouse Gas 38 NOx 37 Diesel Fuel 37 Shutdowns 37 NOx emissions 37 Smog 37 Shutdown 37 air pollution 37 Alternative Fuels 37 tailpipe emissions 37 Drunk Driver 36 pollutant emissions 36 Roadwork 36 Procrastination 36 Dumping 36 Fuel 36 Carbon Dioxide 36 GHGs 36 Restarting 36 Loitering 36 nitrogen oxides NOx 35 Texting 35 Biodiesel 35 Repaving 35 Drunken Driving 35 smog 35 Greenhouse Gases 35 diesel engines 35 Polluted 35 Zero Emission 35 Biofuel 35 Alternative Fuel 35 Slow Down 35 Distracted driving 35 Carbon Monoxide 35 Panhandling 35 Downtime 35 Light Cameras 35 Carbon Emissions 34 Garbage 34 Stopping 34 Downsizing 34 Conserving 34 Gridlock 34 Overtaking 34 greenhouse gas 34 Breathing 34 Seat Belt 34 nitrogen oxides 34 Deadly Crash 34 diesel exhaust 34 fine particle pollution 34 Distractions 34 Crowding 34 Inefficient 34 diesel engine 34 Illegal dumping 33 pollution 33 air toxics 33 Diverting 33 Shutting 33 Overcrowded 33 cleaner burning 33 Revving 33 Smoking 33 Running 33 CO2 emissions 33 Seatbelt 33 GHG emissions 33 Congestion 33 Drunk driving 33 Obsolete 33 Hydrogen 33 Pothole 33 greenhouse gas GHG emissions 33 particulate pollution