The government is failing to do enough to promote the environmental benefits of car sharing, the Liberal Democrats have said.

Coinciding with National Liftshare Day on Monday, the party highlighted official figures showing the extent to which higher levels of car occupancy could reduce the amount of traffic on Britain's roads.

An analysis of parliamentary answers suggested that a 50 per cent increase in car occupancy would result in a 33 per cent reduction in traffic.

And a 10 per cent increase in car occupancy would result in a nine per cent reduction in traffic.

Transport spokesman Paul Marsden said that since 1997 the average car occupancy level has fallen, creating 129 million new car journeys.

"National Liftshare Day is a welcome reminder to all car users to think about sharing journeys," he said.

"Car sharing is sociable, saves money, and reduces congestion and pollution.  It is a win-win situation.

"Yet the government has given little consideration to how we can best use these 'soft' measures to use our road space more effectively.

"And the concept of liftsharing has not been considered at all."

Marsden also called on ministers to "make reducing congestion a real priority and the promotion of car sharing should play an important role".

Ali Clabburn, managing director of Liftshare, added: "This research has highlighted the results that can be achieved by increasing vehicle occupancy figures in the UK.

"Company travel surveys show that around 50 per cent of commuters would share a car if they could find someone suitable to travel with.

"A small amount of investment in supporting car sharing could result in dramatic reductions in congestion and pollution across the UK."