How much will a 56.2-mpg Corporate Average Fuel Economy standard cost consumers? On average, $6714 per car (in 2008 dollars), says the Center for Automotive Research in Ann Arbor, Michigan. "This model requires a 20 percent PEV (plug-in electric) market share to meet the standards-drastic by any measure," CAR says in its analysis.

The Obama administration is expected to formally propose in September the second strictest of four proposed standards to succeed the 2011-2016 ramp-up to 35.5 mpg. Thanks to the rather convoluted math that has plagued CAFE for decades, these numbers do not really mean every automaker's fleet must average 35.5 mpg in 2016 or 56.2 mpg in 2025. CAFE uses an S curve to determine the fuel-efficiency increases necessary across the automotive spectrum.

A 56.2-mpg standard assumes a 5-percent cut per year in CO2 emission in an automaker's fleet. The most lenient proposal would have cut CO2 by 3 percent per year, to 47 mpg by 2025, while the standard that environmentalist groups most favored would have cut CO2 by 6 percent per year, to 62 mpg.

CAR says the 47-mpg standard would have added $3744 per vehicle. A 4-percent per year/51 mpg standard would have added $5270 per vehicle, and the highly green 62-mpg standard would have added $9790 per vehicle.

Shortly before the administration proposed its CAFE standard, a Boston Consulting Group survey found that, based on consumer demand, gas internal-combustion engines will remain the predominant source of power in North America through 2020.

The 2010 North American powertrain mix was 95-percent gas internal-combustion, 3-percent hybrid electric vehicle and 2-percent diesel. In nine years, it will be 88-percent gas if oil costs $130 per barrel, and 85-percent gas if it costs $180 per barrel, BCG says.

Hybrids would account for 7 percent whatever the price of oil, as would diesel at 2 percent and compressed natural gas at 1 percent. Electric vehicles, including plug-in hybrids and such range-extenders as GM's Voltec technology, would take 2 percent of the market if oil costs $130, or 5 percent if it's $180 per barrel. The U.S. market would at least have to quadruple its electric-vehicle consumption in five years to meet CAR's projections for the proposed CAFE standard.

We know what you're asking: Why not diesel? In Europe, the 2010 mix was 46 percent diesel/54 percent gas. "I don't think we're going to bridge that gap any time soon," Xavier Mosquet says about diesel sales in North America versus diesel sales in Europe. Mosquet is senior partner in BCG's automotive practice and lead author of "Powering Autos to 2020: The Era of the Electric Car?"

BCG sees CNG, a negligible part of the U.S. market now, as growing to no more than 1 percent of the market in 2020, whatever the price of oil. It cites the lack of infrastructure, though recent reports that natural gas reserves in the U.S. have been highly overstated will be a bigger impediment. BCG sees gasoline combustion engines as improving faster than expected, while battery technology is improving about as expected.

Internal combustion and plug-in electrics seem to be the powerplants of the future. To the consternation of the hydrogen industry and the California Air Resources Board, Energy Secretary Steven Chu wants to cut federal funds for hydrogen fuel-cell development by almost half.

A National Resource Council study cited in CAR's research shows low-friction lubricants, low rolling resistance tires, better aerodynamics, dual clutch transmissions (DCT), dual cam phasing with continuously variable valve timing, stoichiometric gas direct injection, turbocharging/downsizing, electric assisted power steering (EPAS), reduced engine friction, improved accessories and 5-percent mass reduction would cut fuel consumption by 29 percent at a consumer cost of $2159.

Switching to a clean diesel engine employing low-friction lubes, low rolling resistance tires, better aero, DCT, EPAS, improved accessories, and 5-percent mass reduction cuts consumption by 37.5 percent for $5909. A hybrid with those technology improvements cuts consumption by 43.9 percent costs consumers $6027.

Automakers have been using more high-strength steel to reduce mass while preserving the rigidity of the body structure, though so far, additional standard equipment and safety gear have more than offset any weight loss.

The future of the automobile is clear, though. We'll see better, lighter, and perhaps smaller cars with gas internal-combustion engines, constantly improved after 125 years of development, combined with a slowly, steadily rising share of plug-in electrics-especially those with range-extending engines.

Aside from government tax incentives and some huge, unexpected breakthrough in battery technology, automakers most likely will have to provide "disincentives." By 2025, they'll have to make it less attractive to buy a non-electrified car, padding the profit margins on one to help pay for the other. Also, we'll need more plug-in stations at workplaces and in public locations.

Before you get angry about our proposed new standards, keep in mind that auto industry globalization makes it inevitable. The European Union's 2015 CO2 standard equal 45 mpg, and a proposed 2020 standard would equal 61 mpg. In Japan, the equivalent standard is 47 mpg by 2015, says BCG. In China, where the booming auto industry is helping push up oil prices, the proposed 2015 standard is 36 mpg.