Under a plan announced last week, President Obama plans to cut fuel usage in vehicles. The plan sets a national fuel-efficiency standard starting in model year 2012. That number would eventually reach 35.5 miles per gallon in model year 2016. The standard today is about 25 mpg. But how will the nation respond to the new rules? 1. People may start driving more. We see it every time gas prices go down -- people hit the roads because it's cheaper to drive than to fly. Because cars will get better mileage, the cost of driving will decrease. A 2007 analysis by University of California-Irvine researchers estimated that U.S. fuel efficiency improvements from 2000-2004 led Americans to drive 6% more miles. 2. People may hang on to their old jallopies longer. The new plan estimates that new cars and trucks will cost an average of $1,300 more. Older cars are more likely to cause emissions, defeating part of the purpose of the new fuel plan. 3. Car companies the Obama administration is trying to save may have a hard time adapting to the new rules. GM and Chrysler in particular have businesses focused on relatively fuel-hungry vehicles, and they need to sell off those models before the new rules come into play. Long-term, the new fuel rules could bring about greater fuel-efficiency in the U.S., but the road to adaption will be a long one.