Volvo has finished testing its kinetic flywheel technology, which is fitted to a vehicle’s rear axle and transfers energy generated during braking to a vehicle’s rear wheels.

The automaker’s Derek Crabb, Vice President Powertrain Engineering at Volvo Car Group, said that when combined with a turbocharged four-cylinder engine, Volvo’s Flywheel KERS (Kinetic Energy Recovery System) can improve fuel economy by up to 25% when compared with a turbocharged six-cylinder engine that provides comparable performance. Crabb added the flywheel adds about 80 hp to a turbocharged four-cylinder engine.

Volvo said that because the flywheel generates energy during braking, this technology is most effective in start-and-stop traffic conditions, for example in urban driving situations.

Volvo’s Crabb said the next step for the automaker is to evaluate how it can use this technology in its new vehicles.