An alternative parallel hybrid is the "through the road" type. In this system a conventional drivetrain powers one axle, with an electric motor or motors driving another. This arrangement was used by the earliest 'off track' trolleybuses. It in effect provides a complete backup power train. In modern motors batteries can be recharged through regenerative braking or by loading the electrically driven wheels during cruise. This allows a simpler approach to power-management. This layout also has the advantage of providing four-wheel-drive in some conditions. (An example of this principle is a bicycle fitted with a front hub motor, which assists the cyclist's pedal power at the rear wheel.) Vehicles of this type include the Audi 100 Duo II and Subaru VIZIV concept cars, the PSA Group vehicles Peugeot 3008, Peugeot 508, 508 RXH, Citroen DS5 all using the HYbrid4 system, the Volvo V60 plug-in hybrid, the BMW 2 Series Active Tourer, BMW i8, and the second generation Honda NSX.