RideFlag takes Vehicle Occupancy Detection (VOD) camera technology and puts it into an easy-to-use smartphone application that accurately validates High Occupancy Vehicles (HOV). Solving HOV misdeclaration is key to making congestion mitigation strategies work effectively in order to reduce traffic congestion and the resulting CO2 GHG emissions. Because validation requires only one smartphone, the need for costly hardware, infrastructure, and enforcement associated with other HOV validation solutions is removed. Toll operators can also save millions of dollars of lost revenue that results from toll evasion.