In 2008, green advocates were excited when Volkswagen unveiled the Golf diesel hybrid but it proved to be too expensive to be mass-produced. Supporters are still hoping that the time would come when a diesel engine can be combined with a plug-in hybrid drive.

Last year Volvo planned to make a plug-in hybrid diesel that’s based on its V60. The car manufacturer announced that it already has a prototype built and conducting road tests with it. It also said that it would go into production later this year.

The Volvo plug-in hybrid is expected to do over 100 miles per gallon in regular use. It has a power mode that can be used in inclement weather or when pulling heavy loads. The electric drive powers the rear wheel while the diesel engine powers the front wheel drive. It means that the hybrid car can provide an all-wheel drive when needed.

The Volvo V60 Plug-in Hybrid will be out in the European market in the fall of 2012. Consumers in the United States would have to wait until 2014 in order to purchase one but it would come with a gasoline engine.

Aside from the V60 model, Volvo is also start testing its new plug-in hybrid bus next year. The company said that the bus can operate quietly and emission-free. Three rapid-charge buses will begin their road tests in Gothenburg, Sweden in 2012.

The company has already sold more than 250 hybrid buses. It claimed that it managed to develop the world’s most efficient hybrid system for trucks and buses. Its hybrid buses can save fuel consumption up to 75 percent compared to typical diesel buses.

According to Volvo Buses chief executive officer Hakan Karlsson, decreasing the amount of energy consumption is a top priority for the company. The bus is the world’s most energy efficient form of public transportation and its hybrid bus will become the best green option available. The company continues to look for ways to reduce energy by developing the efficient of its hybrid engines.

Volvo’s plug-in hybrid is based on the end of route charging concept. Charging stations would be installed at the bus terminals. It would only take five to ten minutes to fully charge the battery. The company said that the bus can run on electric engine for up to ten kilometers, which is 6.2 miles. More stations can be installed in urban areas to avoid using fuel in heavy polluted places.