purposes of updating the scorecard, if new hybrid models are introduced during the year, the scale has to be re-calculated to take account of the new arrivals. For the 2011 Scorecard, the Lincoln MKZ Hybrid was rated a 10 while the Volkswagen Touareg Hybrid was rated 0. The Toyota Prius was rated a 9.4. Particulates and Smog-forming Emissions Tailpipe emissions are considered through EPA's air pollution score for each hybrid vehicle and not relatively to the improvement over the similar conventional model. Even though EPA rates air pollution scores for both California and federal standards, the Hybrid Scorecard ratings use only the California emissions certification level in order to introduce the maximum potential to reduce tailpipe emissions . The score is measured in a scale from 0 to 10, where 10 is the best rating and 0 is the worst. Then, using the legal definitions established by the California Air Resources Board (CARB), a zero emissions vehicle (ZEV) is assigned a 10, a partial zero emissions vehicle (PZEV) a 9, a super ultra low emission vehicle (SULEV II) an 8, and so forth. Combined Environmental Improvement Score The final Environmental Improvement Score is determined through the average (and rounded to the nearest tenth) of the values for global warming emissions reductions and tailpipe emissions. As an example, the 2011 Lincoln MKZ Hybrid achieved a 46% reduction in greenhouse gas emissions compared with its sibling gasoline-only model. Because this is the largest percent reduction achieved among all hybrids the MKZ Hybrid earns a global warming emissions score of 10. As a California certified Partial Zero Emission Vehicle, the MKZ Hybrid earns an EPA air pollution score of 9.0. When both scores are combined, the MKZ Hybrid earns an overall Environmental Improvement Score of 9.5. Hybrid value This category measures how cost-effectively a particular hybrid achieves its environmental performance, and the scores vary from "Very Poor" to "Superior." Each hybrid model is evaluated by dividing the estimated cost of hybrid technology used in the vehicle by its reduction in global warming emissions over the conventional model expressed as a percentage. The ratings are assigned to each model based on the resulting incremental cost according to the range values shown in the table in the right. When a hybrid achieves a better smog certification level than its conventional counterpart, the hybrid technology cost should include the cost of any additional emissions controls used