Size matters - smaller cars outcompete the bigger ones in fuel economy

Not often you can visualize the impact of size and weight on fuel economy so transparently as with the latest Volkswagen Bluemotion models. While the new coming Polo Bluemotion has a smaller engine, the Passat and the Golf share exactly the same 1.6 liter Diesel engine.
Interestingly therefore the Passat consumes 15.8% more Diesel, while being 13.7% heavier, 2.3% wider, 0.3% higher and 10.6% slower (0-100 km/h) than the Volkswagen Golf.
So here's a case that make it very evident how efficiency depends on weight and size. Most people probably would have enough space in all of these three cars, a today's Golf almost offers as much space as a BMW 5 series 15 or 20 years ago. So if people really want to save the planet they only have to downsize. And they will not suffer as they typically will get a faster and easier to manoevre car on top.