The great pitfall of government policies, no matter how well-intended they might be, is their inevitable unintended consequences. When those are truly surprising, it's hard to attach much blame to the legislators or regulators involved. However, that degree of indulgence shouldn't apply when the unintended consequences are as obvious as the ones inherent in the new fuel economy regulations that were announced with such fanfare last week. After all, an earlier generation of CAFE standards gave rise to what might just be the classic unintended consequence of recent times: the "SUV loophole" that fed a 20-plus-year SUV fad and dug the nation's oil consumption hole much deeper than it needed to be, affecting oil prices, trade deficits and energy security. Now regulators are proposing the creation of a similar loophole for electric vehicles.

I'm not surprised that the coverage I have read on the latest CAFE debate didn't remind the public of the ongoing consequences of treating pick-up trucks and delivery vehicles differently than passenger cars when the first CAFE standards were established in the 1970s. (That loophole was mostly closed just a few years ago.) Who could have guessed that a provision intended to help small businesses would blow up, because an entire generation embraced deluxe versions of such vehicles as their primary transportation--by the tens of millions--undermining the purpose of the CAFE standards to reduce gasoline demand? When I looked at this several years ago, I estimated that SUVs had increased US gasoline consumption by over 400,000 barrels per day, or roughly 5% of total demand, equivalent to the energy contribution of around 10 billion gallons per year of ethanol.

In this case the problem starts with the evolution of Corporate Average Fuel Economy standards from a tool intended solely to improve US energy security by reducing the consumption of petroleum products in transportation, to one encompassing the greenhouse gas emissions implicated in climate change. Although there are important overlaps between these two goals--keeping a chorus of pundits employed touting them--they are not identical in operation or effect. Consider the specifics of the new CAFE proposal.

The "supplemental notice of intent" from the National Highway Traffic Safety Agency (NHTSA) of the Department of Energy, the body that along with the EPA designs and enforces the CAFE standard, spells out the special treatment accorded EVs in the rules that will be forthcoming. It states that EPA intends to give manufacturers multiple credit for each EV, plug-in hybrid (PHEV) and fuel cell vehicle they sell, starting at a multiplier of 2.0 for EVs and fuel cells and declining to 1.5 by 2021, as if these cars somehow canceled the emissions of more than one vehicle. They also intend to treat EVs and the electric portion of PHEVs as having zero emissions, regardless of how the power they use is generated. So in order to meet the tough greenhouse gas standards that accompany the 54.5 mpg CAFE standard, carmakers will have every incentive to produce as many EVs they can. Unfortunately, it's not obvious that this will reduce emissions in the real world, except in the rare instances when EVs recharge exclusively from renewable or nuclear power, which provide only 30% of our electricity mix today, up from 28% in 2005.

One needn't assume that EVs might be recharged using only coal-fired power to see that they aren't always a big improvement, emissions-wise, over non-plug-in Prius-type hybrids or clean diesels. Using the average US grid CO2 emissions of around 1.3 lb/kWh, a Nissan Leaf getting 3 miles per kWh is responsible for the emission of roughly 200 grams of CO2 per mile traveled. By comparison, a 2011 Prius with its 50 mpg EPA average emits around 196 g/mi. A more rigorous comparison would require a full well-to-wheels lifecycle assessment, but that is precisely what the new CAFE rules eschew in the interest of leaning on the scales to help today's preferred vehicle technology.

Subject to further refinement, this back-of-the-envelope analysis suggests that skewing the new CAFE regulations in favor of EVs isn't going to do much to reduce greenhouse gas emissions. Its main advantage is in reducing oil consumption, since less than 1% of our electricity is generated from oil. But if we only cared about oil and not emissions, producing gasoline from domestic coal--in the same manner as a sizeable fraction of South Africa's gasoline supply--would be equally effective at backing out oil imports. Meanwhile, a gallon of gasoline saved by an advanced internal combustion engine with stop-start technology and other low-cost efficiency features would be worth exactly as much as a gallon saved by an EV, while costing dramatically less. That's especially true when you factor in the $7,500/car EV tax credit, which I can't help thinking will be a prime target when the joint Congressional committee on deficit reduction established by the debt limit bill passed by the House of Representatives last night and by the Senate just a few minutes ago sets up shop this fall.

The unintended consequence that is easily envisioned from this special treatment of EVs is a massive over-investment in a particular and still very expensive vehicle technology, at the expense of other, less costly and more cost-effective technologies. I am entirely willing to accept that EVs represent a major long-term trend in cars, but I don't believe that their development requires fiddling with the CAFE rules in this way. Nor is it obvious that US manufacturers enjoy any particular competitive advantage in producing EVs, which depend on ingredients such as rare earths for which we are even more import-dependent than for oil. If saving oil and emissions is what we really care about, then we are entitled to expect that new fuel economy regulations would focus squarely on those outcomes, without being diverted by the industrial policy fad of the moment. Perhaps this will be one of the topics taken up by the House Oversight and Government Reform Committee of the Congress as it investigates the new CAFE rules.