So how goes the long, steep climb to corporate average fuel economy of 54.5 mpg by the 2025 model year?
Pretty well, according to speakers at a University of Michigan Transportation Research Institute conference last week. But even so, there's no guarantee that the national CAFE will ever hit that mark -- not when you factor in a new president in 2017, changing vehicle mix and volatile petroleum prices.
Actually, 54.5 mpg has always been a mythical beast. It's the estimate of where CAFE would stand by the 2025 model year, based on assumptions about vehicle mix and 4 percent annual improvement.
Ryan Keefe, an analyst at the U.S. Department of Transportation's Volpe National Transportation Systems Center, said a midcycle review due in 2017 could alter the path. The current 4 percent improvement curve is only firm until 2021.
But radical change seems unlikely. That's because the likelihood of large-scale, highly expensive powertrain electrification -- which might stir up considerable political heat -- seems to be receding.
Automakers have proved effective at wringing efficiencies out of internal combustion drivetrains, along with weight reduction and aerodynamics.
More electric-drive features will appear, said Gary Horvat, Denso Corp. vice president of powertrain: "Every one of the manufacturers that we talk to can't get there without some electrification."
But, he said, the push will be for "cost-effective electrification" -- of mild- and micro-hybrid systems rather than electric vehicles and plug-in hybrids.
Sunk cost is another reason that the current target may survive. As Michael Olechiw, director of the EPA's light vehicle and small engine center, put it: "The manufacturers are making a lot of product decisions, and they're spending billions of dollars to meet these standards."
When automakers invest that kind of money in a technology path spanning multiple product cycles, it's no small matter to change it.
Automakers like stability, even if it means pushing to hit a tough standard.