Slowly but surely, natural gas vehicles are gaining momentum. State governments have shown they are particularly interested in integrating their fleets with natural gas powered cars and trucks. That's a great sign for companies like General Motors (GM 0.40%) and Ford (F 0.30%), both of which are growing their NGV offerings in 2014. In this video, Fool.com contributor Aimee Duffy talks to Tyler Crowe about which states offer the most compelling environments for NGVs right now, and what investors need to think about as this trend continues.