France plans to make it easier for Paris and other big cities to introduce London-style urban vehicle tolls in a bid to reduce pollution and congestion, a government source told Reuters on Friday.

Under legislation introduced in 2015, French cities have the right to introduce urban tolls, but only on an experimental basis and for a maximum of three years.

“No city will invest in congestion pricing infrastructure on those terms. The legislative framework is too constraining, it needs to evolve,” said the source.

The Transport Ministry is preparing a decree on congestion pricing as part of a new law on mobility that will be presented this autumn, he said.

Singapore, London, Stockholm, and Milan have all introduced congestion pricing systems, but no French city has done so, although France has an extensive toll system on its highways.

In October 2017, Paris’s deputy mayor for urban planning, Jean-Louis Missika, said the idea of urban tolls was worth considering, but mayor Anne Hidalgo said she did not want a financial barrier to entering the city.

The city has, however, increased parking fees and introduced a sticker system to keep the most polluting cars off its roads on days when pollution levels are high. Hidalgo also said last year that Paris wants to ban petrol- and diesel-fueled cars from its roads by 2030.

Sources close to the city government say Paris transport officials are still studying the idea of tolls, although they are unlikely to be introduced before municipal elections in 2020.