The Victorian Government is sponsoring a trial of two hybrid buses. As the video from the Victorian Transport Department explains, two types of hybrid bus are being trialled: the serial hybrid is more suited to slow routes with many stops, the parallel to longer routes with higher speed.
The series hybrid vehicle is for Ventura Coaches, with the wheels driven only by electric motors. It is claimed to reduce fuel use by 40%. There are 640 lithium ion batteries charged from a 2-litre diesel Volkswagen car engine. The internal combustion engine is much smaller than that normally used in a bus. As this is a full hybrid, the bus could, in theory act as a plug-in hybrid, or pure electric bus, charged from mains power. However, as Victorian electricity is primarily sourced from highly polluting brown coal, this would not have environmental benefits.
The Grendas Bus Service vehicle is a parallel hybrid (similar to a most hybrid cars), built from an Australian made Iveco bus chassis, Volgren Low Floor Route bus body and Cummins diesel Allison hybrid gearbox. This is used as a "Smart Bus" on the Springvale Road 888/889 route.
One aspect of the hybrid buses which is not clear is their fuel source. If the hybrid buses run on diesel they may have little environmental or cost advantages over conventional natural gas powered vehicles.