We might wish progress was faster, but the world’s carmakers are working hard to make motoring sustainable. Fundamentally there are three different things you can do to reduce a car’s environmental impact:

• Go small. Make it smaller and lighter and it will use less energy.
• Go clever. Fit it with the latest technical solutions that can cut energy use.
• Go better. Just get to work and make it more efficient.

Here are six great examples from Frankfurt on how manufacturers are putting these ideas into practice in concept and production cars.

Clever: Opel Flextreme concept

GM has been working on electric cars with fuel-cell power systems long before the fear of climate change became mainstream. But so far, there isn’t a lot to show for it. Flextreme moves the debate on by recognizing that you can have clean, quiet electric propulsion and be flexible about where the power comes from, an idea GM has dubbed “E-Flex”. Instead of a not-yet-practical zero-emssion fuel cell, Flextreme gets its power from a small diesel engine that drives only a generator, not the wheels. The result: ultra-low emissions of 40 g/km (.62 miles) CO2 from technology that’s more or less workable now, in a great-looking vehicle with the space and range of an ordinary car.

Clever: Volvo ReCharge concept

Like the Flextreme, the ReCharge has a 1.6-liter engine that generates electricity to drive the car, with no direct connection between engine and wheels. Unlike the Flextreme, it’s a “plug-in hybrid” that charges its batteries from a standard power point and you won’t need to fire up the engine at all for around 62 miles (100 km). During that time, you’ve got zero roadside emissions — though of course overall emissions depend on how clean the source of the electricity is. The downside is that once the engine kicks in, efficiency is similar to a conventional car at around 35 mpg. The in-wheel electric motors are certainly clever, though.

Better: Mercedes C200 CDI BLUETEC

Want to go green but don’t want to downsize? Well, you don’t have to, when a luxurious, executive-size car like this can manage 39 mpg. Put simply, the idea behind BLUETEC is that a lot of little improvements can make a big difference. It’s a bit like saving power by not leaving your TV on, so you don’t need to switch to a smaller TV. Very few of the many efficiency-enhancing tweaks and improvements in BLUETEC were quite as easy to do as that, but they certainly do make a big difference. Plenty of other carmakers are doing similar things, but few have put as many on sale today (or promised to) than Mercedes.

Better: Ford Focus ECOnetic

Newly announced at Frankfurt, ECOnetic is Ford’s equivalent of BLUETEC. Going on sale soon, this Focus has a conventional 109-horsepower diesel engine that emits 115 g/km (.62 miles) of CO2. Changes include specially developed low-friction gearbox oil, reduced ride height, altered tires and other aerodynamic tweaks. There’s even a redesigned power steering system that runs on reduced power when the driver isn’t actually turning the wheels. ECOnetic versions of the Mondeo and an unnamed car will soon replace the Fiesta during 2008. This is hardly Frankfurt’s most glamorous debut, but it puts greener motoring based on reliable, long-proven technology within reach of millions of people.

Small: Daihatsu Cuore

You don’t have to be a rocket scientist to know that smaller cars need less fuel and less tarmac. But you do have to be a pretty smart engineer to downscale a car without losing character, driving pleasure, comfort, practicality and safety. Daihatsu has a century’s experience of building proper cars at miniature sizes for Japan’s crowded roads. German motorists (it’s not sold in all markets) can now buy Daihatsu's latest, the new Cuore. For 40% of the price of a Toyota Prius, they’ll get a neat four-seater, powered by a standard gasoline engine that will exactly equal the Prius’ CO2 emissions (104 g/km or per .62 miles). The bonus is that it’ll be easier to park (it’s smaller) and when it’s worn out, there are no toxic battery chemicals to recycle. It has to be worth a look.

Small, better, clever: Fiat Panda Aria concept

To round out our list, a car that has a little bit of everything. First of all, it’s based on the Panda, a well-rounded and surprisingly accommodating small car (not sold in North America). Secondly, it has a clever stop-start system that cuts the engine when stationary and instantly restarts it when you’re ready to pull away. And thirdly, it has a new and improved, high efficient, 900c two-cylinder turbocharged engine capable of running on biofuels. The result: very low CO2 emissions at 69 g/km (.62 miles). Notably, most of these technologies are already in production in other places. So why can’t you buy one? Purchase cost and drivability would probably be the biggest obstacles to sales success. What price are you willing to pay for lower emissions?