Car companies are taking several different directions towards making their cars of the future more efficient.
Some are going down the hybrid route, using electric motors to assist and occasionally take over from gasoline engines. GM is taking a two-pronged approach, with the range-extended Volt and a future Cruze diesel. The former is great in the city, the latter will excel on the freeway.
Mazda will be going diesel too, but it's putting most of its chips on making the good ol' gasoline engine ever more efficient using its SKYACTIV technology. The 2012 Mazda3 SKYACTIV-G will get 40 MPG on the highway - right up there with the best.
How do you get 40 MPG highway?
There are several factors contributing to the Mazda's great economy, according to Automotive Engineering Online.
The first is one of the simplest ways for a carmaker to increase economy - selling small, light cars. A SKYACTIV engine in the smaller Mazda2 has logged the equivalent of 70 MPG highway - that's the benefit of running a small, efficient engine in a small, lightweight car.
The 3 isn't a big car either so it's already well-placed to make use of an efficient engine.
Little improvements, everywhere
The engine itself is high-tech too. It's a long-stroke engine which is good for torque at lower revs, which as we know is more beneficial in most day-to-day driving. It's also relatively high compression, meaning less fuel is burned with every bang. Evaoporative cooling ensures knocking is never a problem.
Variable intake and exhaust valve timing help keep the engine in its most efficient cycle whatever the driving conditions. Late intake valve closing on very low load reduces pumping losses - the engine's energy lost to drawing in and expelling air.