A rear view of two Tesla cars at a Tesla car dealership in Los Angeles, Calif., on June 23, 2009 © MCP, Rex Features

American drivers, meet the 4.2%.

That's the share of the 14.44 million cars sold in 2012 that had either hybrid, pure electric or clean-burning diesel engines, according to HybridCars.com and Baum & Associates. Yes, it's still fewer than one in every 20 cars -- which makes the furor over The New York Times' Tesla (TSLA) test drive all the more puzzling.

But make no mistake -- that number is steadily rising, with help from both automakers and government incentives.

The Energy Information Administration at the Department of Energy notes that more than 12 million alternative-fuel vehicles were on American roads in 2011. That includes 10 million ethanol/flex-fuel vehicles and 2.1 million gas/diesel-electric hybrids. This alt-fuel fleet is part of the reason the U.S. imported just 41% of its oil in the first five months of 2013, according to DOE, down from 65% in 2005. Alt-fuel cars alone can't drive America to its long-sought goal of energy independence, but they can bring it closer.

Overall, they're still a pittance compared to the 210 million conventional-fuel vehicles driving around, but the EIA expects the alt-fuel contingent to grow to 15 million by year-end. While cars that, theoretically, can handle an E85 ethanol blend (15% gasoline, 85% ethanol) still make up the majority of those gains, the number of electric-gas hybrid cars is set to double by 2017, with the number of plug-in hybrids and plug-in electric cars also expected to rise dramatically.

Longer-term, the number of hybrids and plug-ins traversing the U.S. is expected to rise 23.2% and 17.9%, respectively, by 2040.

But the current class of alternatives to straight gas-powered engines is likely to get a lot larger. The EIA envisions a future in which vehicles using gasoline, methanol and hydrogen fuel cells share the road with vehicles that run on natural gas and propane fuel blends. That means the ranks of gasoline-powered cars will increase only 0.5% by 2040, with conventional light truck sales stagnating over the same period.

However, this also supposes a future in which the average mileage for a gas-powered car surges to 39 miles per gallon for hulking utility vehicles and 54 mpg for subcompacts, while hybrids range from 52-75 mpg (gas-electric) and 61-98 mpg (plug-ins). For the sake of comparison, the most efficient gas-electric hybrid on the road today -- Toyota's (TM) Prius C -- currently manages the 51 miles per gallon that the EIA expects of large hybrid SUVs and vans in 2040.

This also assumes U.S. car buyers will stop freaking out long enough to buy in. Although marketing firm Mintel says alt-fuel vehicle sales grew more than 70% last year and it expects hybrid and electric car sales alone to increase 14% in 2013, buyers' fears are still stifling sales.

A Mintel survey found that 34% consumers ages 25 to 34 think that "it is easy to make back the extra money spent on a hybrid car in savings at the pump," despite evidence to the contrary. But "the 'live for today' mentality that prompted the rise of SUVs has disappeared," says Mintel analyst Colin Bird. "Consumers today demand products that promise protection and durability." When Americans prize longevity and efficiency over sheer size and brute force, that favors alternative-fuel vehicles.

The electric sockets on a Ford (F) Fusion Energi, General Motors (GM) Chevy Volt and Prius plug-in still make consumers nervous, however, with 87% worrying how long their battery will hold a charge, 86% fearing they won't be able to find a charging station once they leave home and 85% nervous that their car will take too long to recharge, according to Mintel.

Most people still have one key issue with alt-fuel vehicles even though they've been around for more than a decade: price. Mintel found that the average consumer is willing to spend $2,000 more to upgrade from a conventional car to an electric-only version of the same car. The problem is that plug-in hybrids and electric cars cost between $10,000 and $20,000 more than their conventional counterparts, and so far the plug-in hybrids don't offer enough nonelectric mpg, while the electric cars don't offer enough range or speedy recharging options to make the switch worthwhile.

Although enough Americans have made the jump to alt-fuel vehicles in the last decade to raise the category's market share from less than 0.5% to 4.2%, the cost of that change is proving prohibitive for all but a few automakers. Toyota, for example, still holds a 67% share of the U.S. hybrid market largely because it can keep a Prius' base price below $25,000. Ford, whose hybrid share is little more than 15%, is starting to get the picture and offering its C-Max and Fusion hybrids at around the same price.

Both federal and state agencies are trying to goose the market by pointing buyers toward laws and incentives that cut the cost a bit, but government investment in the auto industry has been a sore spot of late. As Chrysler introduces a diesel-powered Jeep Cherokee this year and GM offers a diesel Chevrolet Cruze, some car buyers are still irate about the government bailout money they received a few years back to keep afloat. While some of Tesla's New York Times controversy was tied to the electric car company's own government backing, electric carmakers like Fisker and Coda that have sputtered despite receiving federal funds are also coming under scrutiny.

Is it still energy "independence" if that new energy source is being subsidized? Considering how much cash the federal government has thrown at the automakers regardless of the fuel source they use, maybe it is. And if alt-fuel cars can just maintain their momentum, they'll earn their independence from Uncle Sam's allowance.  

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This article is part of an MSN Money special report on America's quest for energy independence. Up next: 12 weird energy sources that could change the world.

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