President Barack Obama on Friday announced a deal struck with 13 automakers that will double the fuel efficiency of today's cars by 2025.

News of the deal began leaking a few days earlier, inspiring several industry experts and news organizations to speculate on the billion-barrel-of-oil question: What are the technologies automakers will use to meet the new standard of 54.5 miles per gallon by 2025?

We can see ample evidence of the different elements automakers will utilize to meet the new goal. Ford, for example, is currently selling and developing a mix of electric, hybrid and plug-in hybrid vehicles. Nissan is touting its all-electric Leaf, which it is calling the nation's first mass-marketed all-electric vehicle. General Motors is using turbochargers from Honeywell to help achieve a 42 mpg of its Chevy Cruze, which Honeywell described as June's best-selling vehicle in the U.S. The turbochargers can improve fuel economy up to 20 percent on standard gasoline engines, Honeywell said Friday, and up to 40 percent in diesel vehicles.

From an engineering perspective, automakers can currently pull off 40 mpg, but the new standard is "a gas station too far," wrote Alexander Wolfe, an engineering and technology journalist who serves as content director of Design News, a technical publication aimed at design engineers and engineering managers. "Still, if we attack the challenge on multiple fronts, we can get close."

Wolfe listed several target areas, including what he called the single most important component: materials. Making cars lighter by using advanced plastics or fiber-reinforced components will go a long way toward making vehicles more efficient, but they often carry a heftier price tag than the materials they would be replacing. UPS is venturing down this road by testing a prototype delivery truck made with lightweight plastic in place of aluminum sheet body panels that uses about 40 percent less fuel. UPS hasn't revealed the price tag but described the upfront cost of the redesign as very affordable.

The types of vehicles consumers want to drive, Wolfe noted, along with the tires that will carry them will all play a role in pushing automakers toward that 54.5 mark.

In contrast, Roland Hwang, director of the Natural Resources Defense Council's transportation programs, believes the automakers' arsenal is already well-equipped with affordable, existing technologies that can achieve the 54.5 Corporate Average Fuel Economy (CAFE) without giving up performance.

In a blog post, Hwang outlined four key technologies that will play a role during the transition to 54.5 mpg, including several that overlapped with Wolfe's list:

1. Improved conventional gasoline engine vehicles through such technologies as direct fuel injection, turbocharging, cooling and boosting the exhaust gas, and adding stop/start systems that shuts the engine off at idle.
2. Improved, lower-cost hybrids technologies called “parallel 2-clutch” systems that Hyundai, VW, Nissan are introducing now into the marketplace.
3. Plug-in hybrids and battery electrics with lower cost, advanced lithium batteries.
4. Lightweight, high strength materials to reduce mass 10 percent from 2016 levels, consistent with auto industry trends.

Michael Kanellos of Greentech Media offered a few off-the-beaten-path solutions to the 54.5 mpg dilemma, some of which fall into the categories already mentioned. Hemp, he wrote last week, could maybe be used as a substitute for other materials. Companies are also developing "wacky transmissions" that could one day play a role in improving fuel economy, such as Fallbrook Technologies' transmission system that uses balls instead of gears to improve mileage by up to 15 percent.

Waste heat may also become a fuel source to power vehicle systems, such as air conditioning.

"Tempronics, Phononic Devices and Alphabet Energy are also working on devices for converting waste heat into electricity," Kanellos wrote. "(Tempronics -- like tempura with electronics -- is particularly focused on cooling, as well.)"

_{Photo courtesy of Ford.}