Railways are one of the most energy efficient forms of transportation, with the lowest volume to emissions ratio. Energy efficiency in railways deals with reducing the amount of energy consumed by rail travel and reducing carbon emissions and other pollutants that occur due to the process. AEA Technology conducted a study analyzing the difference in environmental impact between a Eurostar train and an airline journey between London and Paris. Trains were found to emit 10 times less CO2 per passenger than a plane. In the US railways account for just 4% of the overall vehicular emissions generated. Freight transport in the railways sector is also immensely popular. The high volume, low value of transporting freight via this mode of transportation makes it economically feasible.