Although there are a handful of economists and industry leaders crying foul, the new fuel economy standards for heavy duty trucks proposed this week by the Obama administration are being met with open arms by many who say the rules have been a long time coming. "This is a historic first step towards putting the energy hogs of America’s roadways on a much-needed diet," Rich Kassel of NRDC wrote on Monday. And according to the New York Times, the American Trucking Association approved the approach, preferring it to a fuel tax or a rigid CO2 reductions requirement.

The proposed efficiency standards are the first ever for heavy-duty trucks and would apply to three categories:* combination tractors, heavy-duty pickups and vans, and vocational vehicles (eg. dump trucks and cement mixers); covering new vehicles manufactured between 2014 and 2018. But unlike CAFE standards which employ straight ahead miles-per-gallon requirements for passenger vehicles and light trucks, the standards proposed this week employ a mix of fuel economy and greenhouse gas emissions requirements.

“These are performance standards that allow flexibility; they are not one size fits all,” EPA Administrator Lisa P. Jackson said on a Monday call with reporters.

“In addition to cutting greenhouse gas pollution, greater fuel economy will shrink fuel costs for small businesses that depend on pickups and heavy duty vehicles, shipping companies and cities and towns with fleets of these vehicles," said Administrator Jackson.

On the call with reporters, both Administrator Jackson and Secretary of Transportation, Ray LaHood, emphasized that these advancements could be made with existing technologies. So what exactly are those existing technologies, how do they work and how much fuel will they save? Based on a report from the National Research Council, the Union of Concerned Scientists says fuel reductions will come from the following places:

1. Clean-idling and hybrid technologies: Long-haul trucks emit 11 million tons of CO2, 200,000 tons of NOx, and 5,000 tons of particulate matter into the air annually just while idling. So reductions in fuel consumption while idling also benefits local air quality. Hybridization and clean-idling or anti-idling technologies can reduce fuel consumption by 6% to 10%, depending on the application. Clean-idling technology allows truck drivers to use battery power to heat, cool and power accessories in the truck cab as they rest and sleep. Hybrid-electric systems are great for trucks that make short trips around town and may idle while they work (eg. utility trucks, delivery vehicles). Companies like UPS and FedEx have both invested significantly in hybrid electric and electric drive trucks that capture energy from regenerative braking.

2. Fuel efficient tires and wheels: Yawn, right? Wrong.  Replace the standard dual-tire configuration with lower rolling-resistance and wide-base single tires and automatic tire-inflation devices that keep tires at optimum tire pressure can reduce fuel consumption by up to 11 percent. educe wasted energy as tires roll down the road.

(Image: Union of Concerned Scientists, click to expand)

3. Reducing weight: Lighter materials like aluminum, high strength steel and carbon fibers, can account for a modest 1% fuel reduction.

4. Aerodynamics in both cab and trailer: This one is a double-whammy because improved aerodynamics in both the cab and the trailer. For the cab, the UCS says shaping based on wind tunnel testing and computer simulation, can account for 3% to 4% fuel reduction, useful for trucks moving at highway speeds. On the trailer side of the equation, it's all about filling the gaps between the back wheels and also between the cab and the trailer. This can account for up to 8.5% reduction in fuel.

5. Engine efficiency and clean diesel technology: At five to fifteen percent, the most significant reductions in fuel consumption across the board may be in making engines more efficient. Supporters of so-called "clean diesel" technology say adding turbos and advanced fuel delivery systems, replacing inefficient (and leaky) air conditioners and making other adjustments to the efficiency of diesel engines can reduce fuel by as much as 20 percent.

6. Advanced transmissions: Replacing standard dual-drive axles with single-drive axles and using automated manual transmissions that optimize shifting while maintaining efficiency advantages of manual transmission can save five to seven percent of fuel used.