[rice_classic]

Last one I promise... you should still be reading, this is important.

Assuming the model lasts until 2020, the Mazda6 would have to achieve fuel economy figures in the high 40 mpg CAFE range. Engineering a low volume, niche market wagon for sale in America that would be subject to increasingly tough targets is arguably beyond their means, especially given the small volumes the car would sell in. Instead, Mazda offers the CX-5 crossover. Aside from being classified as a crossover, with all the CAFE advantages built in, the CX-5 is able to sell in economically viable volumes not just in the United States, but across the globe. The realities of CAFE have likely made sales of the third generation Mazda6 wagon impossible in the United States.
CAFE's other victim is the compact truck segment. Many consumers don't need a full-size truck (whether they acknowledge it or not), and the Ford Ranger, along with GM's own compact pickups, had respectable followings among consumers looking for a smaller fuel-efficient pickup.
But the Ranger happens to fall into the "dead zone" of the CAFE footprint formula. Both curve graphs show a flat line at 55 square feet; in practical terms, a Mercedes-Benz S-Class carries this footprint. The Ranger, even in SuperCab configuration, has a footprint of 50 square feet, just short of the magic number. The best Ranger, fuel economy-wise, was a 4-cylinder manual truck, returning 22/27 mpg IRL; a respectable number, but one only available in a configuration that a minority of buyers would opt for. Equipped with a V6 and an automatic transmission, it would only return 14/18 mpg IRL, a figure that can be equalled by certain version of Ford's V6 and V8 F-150 full-size pickups. By 2025, a theoretical Ranger with a footprint of 50 square feet would have to achieve fuel economy somewhere approaching 50 mpg CAFE. The 75 square foot F-150 would only have to reach in the high 30s CAFE.
Ford will offer a new Ranger in world markets, but again, it won't come here. GM, on the other hand, plans to offer their new mid-size Colorado and Canyon trucks here, but the reasons for Ford and GM's divergence aren't as cut and dried as they are in the case of Mazda and Volvo. Ford has decided to offer full-size trucks exclusively, with the V6 options as a means of attracting economy-minded buyers, and perhaps taking advantage of CAFE regulations (not to mention, sell more F-Series, which are immensely profitable).
GM's strategy is to forgo to advanced V6 powertrains that Ford offers, and market their full-size trucks alongside their smaller stable mates. If Ford offered a Ranger, it could theoretically cannibalize sales of the lower end F-150s, while muddling their marketing message. GM will presumably have no such conflict. Chrysler is rumored to be taking a third route; offering advanced V6s in their RAM trucks, while exploring a car-based compact pickup, possibly based off of a Fiat product. A truck like that would be a huge boon as far as CAFE compliance goes, and put a decisive nail in the coffin of the Dakota, which offered a V8 engine in a compact body.
Cui Bono

In the trial of Sextus Roscius, a young Cicero defended him by posing a famously concise question; "Cui Bono?", or "who benefits?" CAFE merits a similar line of inquiry.
When examined side by side with European emissions standards, the economics of CAFE become more transparent. EU are relatively straight forward by comparison. Tailpipe CO2 emissions are measured and a de facto consumption tax is levied based on a vehicle's output. There are no footprint formulas or regulatory loopholes that can be manipulated, though there are different standards for diesel and gasoline engines. Either way, the principle is the same; if you want a bigger, more powerful engine, you will have to pay for it via increased taxes. The most tangible examples of these policies in effect are the newly downsized motors being fitted in American-sized cars, like the 1.0L three-cylinder Ford Mondeo (our Fusion).
On the other hand, a consumption tax related to the profligacy of their vehicle would be disastrous to the Big Three. Full-size trucks, rather than cars, are the profit-makers for the Big Three, and no segment has more to lose from tough CAFE standards. The official line is that the big pickups and SUVs have to make up the most ground when it comes to fuel economy, so they are given more leeway with the regulations.
But the reality is that Detroit's car makers need trucks to be affordable to stay in business. CAFE compliance for full-size trucks is a major topic in the auto industry, with concerns about rising costs being a major bugaboo for the Big Three. Ford is said to be moving to an aluminum body for the next F-150, while various reports have claimed that compliance with CAFE 2025 standards could add as much as $15,000 to the cost of a full-size truck. This kind of financial burden would make pickup trucks unaffordable to a significant portion of its customer base, and erode a massive source of profits for American automakers. As Niedermeyer noted, full size trucks would "…become a purely professional purchase, bought only by those who use them for work or by the wealthy." A European-style consumption tax based on emissions of fuel efficiency would be devastating for the full-sized truck market, and it's hardly a coincidence that CAFE is structured in such a way that best protects these vehicles.
In this context, it's easy to see why the two major dissenters from the 2025 CAFE rules were Volkswagen and Mercedes-Benz. Representatives from both companies spoke out candidly about CAFE, with a Volkswagen spokesman stating

"The proposal encourages manufacturers and customers to shift toward larger, less-efficient vehicles, defeating the goal of reduced greenhouse-gas emissions."

Mercedes-Benz was equally forceful, claiming that CAFE

"clearly favors large SUVs and pickup trucks. Our customers expect a range of vehicles from which to choose so this program creates a very real disconnect between government regulation and customer demand."

Europe's own Euro VI standards measure a grand total of 18 pages in PDF format, and are generally regarded as stricter than CAFE. That, combined with the substantially more egalitarian nature of the consumption tax model employed by Euro VI brings the legitimacy of CAFE into question even further.
Ironically, CAFE has much in common with the chicken tax, which is erroneously cited as being the sole impediment to the success of compact pickups in America. Both are horribly protectionist, anti-market laws that restrict consumer choice and give an unfair advantage to homegrown manufacturers. But at least the chicken tax compelled the OEMs to build compact pickups Stateside. Under CAFE, there isn't just no reason to do so – there is every reason not to do so.