The global economic slowdown has meant that many car manufacturers have decided to stay away from this year's Tokyo motor show. But a selection of eco-friendly two-wheeled vehicles are helping to fill the void and show off their green credentials.

Two-wheeled vehicles generally require less energy than four wheels, allowing electric bikes in all shapes and sizes to attract attention at the 41st annual Tokyo motor show.

Some electric bikes can run for nearly 50 kilometers on just one charge, with a top speed of over 30 kilometers per hour.

Motorcycle giant Yamaha realized their potential in 1993 when it developed an electrically assisted bicycle, the first company to do so.

Its latest model, the PAS, is on the market for about one-thousand US dollars.

Satomi Okumura, PR of Yamaha Motors, said, "There are still many challenges that we need to sort out. But we see the potential of the electric two-wheeled vehicle in the international market in the long run."

The company also exhibited conceptual electric commuter vehicles, with futuristic designs aimed at appealing to a wide range of age groups.

As consumers take environmental and health concerns on board when making purchases, the demand for electric vehicles is up.

The sales of the PAS rose from 3,000 in 1993, to over 300-thousand in 2008.

There is huge potential for international growth in this sector.

However, there are also challenges, as regulations governing the power and format of electrically assisted bicycles vary greatly from country to country.