100 miles per gallon

A experimental version of a 2006 Toyota Prius sedan modified by US researchers at the National Renewable Energy Laboratory (NREL) has achieved a record 100 miles per gallon.

The plug-in version of the sedan runs the initial 60 miles mostly on battery, with the remainder achieved under engine power.

The sedan's performance more than doubles the fuel economy of a standard Prius, which is rated at 48/45mpg. Additionally, it is a five-fold improvement over the 20mpg average that passenger cars and light trucks in the US achieved in 2007.

The standard Prius runs on electricity at low speeds, then the batteries and the petrol engine share the work. The batteries recharge automatically as the car operates.

NREL researchers added several features to the plug in Prius to break the 100mpg barrier.

First, they added a plug so that the vehicles batteries could be recharged directly from a standard electrical outlet. Next, they dropped in a larger lithium-ion battery that allows the car to operate on electricity for longer trips. Finally, they incorporated a rooftop solar panel that charges the battery while the car is driving or parked outdoors, adding five miles to the vehicle's range.