The university city of Tubingen, in southwest Germany, is testing free public transportation for all residents. Two weeks ago, the city began a two- year pilot project using its own funds to provide free rides on Saturdays. The aim in Tubingen, Mayor Boris Palmer says, is twofold: to lower emissions and reduce travel costs for people on low incomes.

There is a proposal to test free public transport in four other cities in Germany, which faces European Commission fines for breaking air pollution laws.