As traffic and other sources add more ozone-forming pollutants into the air, ground-level ozone worsens. Motor vehicles are responsible for nearly 50% of smog-forming volatile organic compounds, more than 50% of nitrogen oxide emissions, and approximately 50% of toxic air pollutant emissions in the United States (EPA, 2014) . In the United States, there are more than 210 million cars and light trucks on the road, with carbon monoxide emissions a whopping 75% (EPA, 2014). Between 1970 and 2005, Americans' increase in travel increased by 178% and continues to increase at a rate of 2-3% each year (EPA, 2014). Starting in the late 1980s, America's love of large vehicles began with a significant increase in vans, SUVs, and pickup trucks on the roads. In 2000, these “light trucks” accounted for about half of sales of new cars, which on average consume more gasoline per mile and contribute three to five times more pollution than cars (EPA, 2014)