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Zero emissions vehicles are referred to as carbon negative vehicles or that emit less pollutants than other vehicles can be referred to as carbon neutral or semi zero-emissions vehicles. Examples of semi zero-emissions vehicles include Natural Gas Vehicles since they are not so carbon positive, vehicles in the Euro 6 emission standards since they make use of catalytic converter and Exhaust gas recirculation systems and Hybrid electric vehicles since they can be driven in pure electric mode and in dual mode thereby reducing emissions by 50%.