So auto makers in the EU are scrambling for ways to keep their new cars on the right side of the law. Making cars lighter is one of the simplest ways of gaining that edge, and European car makers are finding ingenious ways to do that without making cars less safe.

Unbeknownst to most drivers, the floors of their cars are layered with asphalt or other heavy materials to absorb engine noise. While this insulation method lets drivers zip down the highway with no more than a quiet hum, it also adds to the car's overall weight, sucking more power and thus more fuel.

To solve the problem, a team of French, Belgian, and Italian researchers began a project with the simple name "E! 2411 ERTAC." Their mission? To make the sound insulation in passenger cars between 30 and 50 percent lighter, thereby cutting vehicle weights and saving fuel -- but without reducing acoustic comfort levels for the car's occupants.

The anatomy of fuel efficiency

Only 12 to 20 percent of the fuel burned by an internal combustion engine is actually used to propel the vehicle. About two-thirds of the total energy is thrown off as heat via the exhaust and coolant systems. Of the one-third that is converted into mechanical energy, a considerable amount is lost to friction in the transmission and other parts of the drive train or swallowed up by the alternator, air conditioning, and other accessories. So-called "standby losses" also occur as the system compensates for engine friction and cooling during idling and deceleration. That leaves the fraction of the fuel that moves the car from Point A to Point B.

In the real world of internal combustion vehicles, increasing fuel efficiency is an incremental process. That makes each of these energy losses a target for improvement. All of them, however, boil down to two basic goals: making the powertrain more efficient, and reducing the work the engine has to do.

On the system efficiency side, regenerative braking and systems that automatically shut the engine down while idling have given European auto makers significant gains. Other opportunities come under the heading of "road load": aerodynamic resistance (the coefficient of drag, or COD, familiar to Formula One aficionados), rolling resistance (the energy sucked away where the rubber meets the road) , and inertia -- aka weight.

Sounding out Ways to Keep Off the Weight

To begin with, the researchers made preliminary measurements on existing vehicles. They analyzed floor panels, dashboard, and other parts of the car chassis for sound insulation, absorption, and damping. They also tested the raw materials the parts were made from. Then, in order to define and quantify acoustic noise behavior without being bogged down in cumbersome physical tests,       developed computer simulation techniques for predicting how lighter materials would perform.

"The manufacturers drastically reduced the time schedules for new car models," said Maurice Fortez, director of Trèves Group, a Paris-based automotive supplier that was the main partner on the project. "So instead of using a slow, time-consuming experimental approach to car acoustics, we switched to developing simulation techniques using proven models to predict the behavior of materials for sound insulation."

These techniques were indispensible to the success of the project, and will be extremely useful for automobile manufacturers, Fortez added. "The simulation of the acoustic performances of car components in the early stages is critical for reducing prototyping costs and improving noise levels inside and outside the car."

In the end, the team -- which also included Esi, Microdb, and Inter AC in France, San Valeriano in Italy, and Huntsman Performance Products in Belgium -- exceeded its goals by a considerable margin. Layering compressed felt with low-density felt reduced the weight of sound insulation by 50 percent. Manufacturing parts that require elasticity from foam textile waste cut the weight by another 25 percent -- with the added benefits of recycling spent materials and bringing down cost. "Through this approach, we even managed to design thinner treatments for sound insulation in the early stages of the process, with the expected mass reduction," added Fortez.

Coming Soon to a Peugeot Near You

The computer-simulated results were then validated on a real-world Citroen C4. "There is a saving of about 8kg on the weight of the complete car," Fortez explained. "The original weight of the insulation was 11.3 kg, but the new technology weighs only 3.4kg." When their results were applied to a physical prototype made by Renault, the overall weight of the vehicle had been reduced by 6.7 percent.

Peugeot is now in the process of manufacturing a prototype. "Peugeot wants to use this technology for its new 207 model," said Fortez. "The company is very much interested in reducing car weight significantly, and wants to verify the results."

Of course, there are other approaches to dampening engine noise. As anyone who has ever had a Prius sneak up on them in a crosswalk can tell you, electric vehicles don't need a whole lot of sound insulation. Still, there are going to be plenty of gas and diesel vehicles on European roads for the foreseeable future -- and where CO2 emissions are concerned, every little cut helps.