The European Commission has today proposed to take into account the effect of trailers on the CO2 emissions of heavy-goods vehicles in road charging schemes that differentiate tolls based on vehicles’ CO2 emissions. Although a trailer does not consume energy by itself, towing it requires energy from the vehicle to which it is attached. Efficient trailers can benefit both conventional vehicles, by reducing fuel consumption and therefore CO2 emissions, as well as zero-emission vehicles, by increasing their range. (....)