"Previously, when a manufacturer had a single number target, you had two choices of how to improve fuel economy to hit that target," says Michael Love, Toyota USA's national manager of Regulatory Affairs and Powertrain Planning. "You could apply technology to a given size truck to make it more efficient, or you could build smaller trucks. Under this new footprint-based program -- depending on whether the curves set by the government are truly size neutral -- there is little or no benefit to building smaller trucks. Your only options are to apply technology and make the vehicles lighter through vehicle design and materials technology, while keeping the same size."

He adds that the 2012-2016 rules require a very aggressive 4.0-4.5-percent annual increase. "With a five-year product cycle between major changes, every time you have a major change, you will need more than a 20-percent increase in fuel economy. What technologies will get you a 20-percent increase? And what will you need for your next 20 percent?"

The rules for 2017-2025, to which the manufacturers have nominally agreed, also require about a 4-percent annual increase for cars. Full-size trucks get no increase through 2020, after which their annual rate of increase will also be about 4 percent for 2021-2025. "That was negotiated with the government to benefit full-size pickups," Love explains, "and there are some yet-to-be-defined bonus credits for full-size hybrid pickups."

Do truckmakers believe they can meet these incredibly aggressive requirements without losing important capabilities and/or driving costs (and therefore retail prices) through the roof? They all say they can and will, but with reservations.

"Arguably, there is a lot of available technology," Love responds, "but the biggest question is the cost. All the cheap technology has already been adopted. We're moving into much more expensive technology, and there's always a debate about what those costs will be -- there are huge differences of opinion between costs as estimated by the government and as estimated by the manufacturers -- and therefore a big question about whether the public is willing to pay for it."

"It is a great challenge for engineers," says Cairns. "Do we know how to do it today? Not really. There is technology that can get us there, but not in a cost-effective manner. If we would just apply known technologies now, we would price ourselves out of the market. So the answers that exist today are not going to be the right answers as we move forward. We have to invent things, come up with new creative ideas, as well as improvements and cost reductions to known technologies, plus the weight reductions and aerodynamic improvements we have been doing over the years. No doubt it's a big challenge, but Ram trucks will find a way because we want to provide what our customers want."

"In one sense, it's a very simple formula to improve fuel economy," Ford's Lewis asserts. "Get weight out, improve rolling resistance, get better aerodynamics, get rid of parasitic losses in the systems and squeeze as much efficiency as possible out of your powertrains.

"We can figure out how to do it, but it will be costly. Technology needs to be developed. We're capable of developing it, but how much investment and variable cost can we put into it? Our business is hugely competitive from a cost and investment perspective, so the bigger challenge is figuring out how to stay in business while implementing it.

"Everyone is faced with the same challenges," he concludes. "We all focus on and will implement fundamentally the same technologies, and we can't lose capabilities. Customers buy trucks for capabilities. So whoever figures it out, executes best, and implements most efficiently with the best business plan will win. We're hopeful that will be us."

And if it turns out that it simply can't be done? We love former GM product guru Bob Lutz's take on CAFE a few years ago, when he still worked for GM:

"If something is impossible," he said, "nobody will do it. And when they get to the point where the legislation is tantamount to saying that cars may no longer touch the road surface because we don't want to deteriorate the infrastructure, so we're mandating that by 2015, all cars have to hover off the highway by 2 inches, I think, well, that's nice. So [if CAFE gets to that point], I won't worry about it. I'll just know it's that it's physically impossible, so something is going to give before we get there."