since the structures of nedc and wltp are different, the values obtained can differ one from the other even if a same is car being tested. as wltp reflects more closely on-road going conditions, its laboratory measures of co emissions are usually higher than the nedc. a vehicle’s performance does not change from one test from the other, simply the wltp simulates a different, more dynamic path, reflecting in a higher mean value of pollutants. this fact is important, because the co figure is used in many countries to determine the cost of vehicle excise duty for new cars. given the discrepancies in between the two procedures the unece suggested the policymakers to consider this asymmetry during the transition process. for example in the uk, during the period of transition from nedc to wltp, if the co value was obtained under the latter, it must be converted to a ‘nedc equivalent’.