UMD collaborative study finds that fuel efficiency of one car in household may be cancelled out by next car purchase A recent collaborative study led by researchers from the University of Maryland (UMD) College of Agriculture and Natural Resources found that consumers tend to buy something less fuel efficient than they normally would for their second car after buying an eco-friendly vehicle. While this sounds like an all-too-logical conclusion, the study reports a 57% reduction in the benefits of driving the fuel efficient car for carbon emissions purely based on the purchase of the second vehicle. Since about three-quarters of cars are purchased into multi-car households, these findings could have major implications for carbon emissions, and especially for the design of carbon mitigation programs like Cash-for-Clunkers and Corporate Average Fuel Economy (CAFE) standards that aren’t taking into account the decisions of consumers with multiple vehicles, the researchers said.