Development of vehicles that can run on alternative fuels is driven by the need for new energy sources due to limited crude oil reserves. Alternative fuels like natural gas, propane, methanol, and electric vehicles are being studied to improve air quality. Traditional focus on reducing tailpipe emissions has been successful, but further reductions won't make a big difference. Using fuels with lower chemical reactivity can help reduce ozone formation, a major air quality challenge in the U.S.