The new rules also introduce the footprint model for cars as well as trucks, where if a manufacturer makes more large cars and trucks they will be allowed to meet a lower standard for fuel economy. This means that an overall fuel efficiency for a particular manufacturer nor the fleet as a whole cannot be predicted with certainty since it will depend on the actual product mix manufactured. However, if the product mix is as NHTSA predicts, car fuel economy would increase from a current standard of to in 2011. The new regulations are designed to be "optimized" with respect to a certain set of assumptions which include: gas prices in 2016 will be $2.25 a U.S. gallon (59.4¢/L), all new car purchasers will pay 7% interest rates on their vehicles purchases, and only care about fuel costs for the first 5 years of a vehicle's life, and that the social cost of carbon is $7 per tonne of CO2. This corresponds to a global warming value of $4.31 savings a year per car under the new regulations. Further, the new regulations assume that no advanced hybrids (Toyota Prius), plug-in hybrids and extended range electric vehicles (Chevrolet Volt), electric cars (Th!nk City), nor alternative fuel vehicles (Honda Civic GX) will be used to achieve these fuel economies. The proposal again explained that U.S. law (49 U.S. Code § 32919) requires that "a State or a political subdivision of a State may not adopt or enforce a law or regulation related to fuel economy standards or average fuel economy standards", and explained that laws or regulations applicable to motor vehicle greenhouse gas emissions are related to fuel economy standards.