Aimed at reducing pollution and noise from the Boulevard Peripherique -- one of Europe's busiest roads -- the restrictions will come into force "a few weeks after the Olympics Games," deputy mayor for transport David Belliard told reporters.

The 35-kilometre (22-mile) Peripherique -- widely known as the "Periph'" -- is used by around 1.2 million vehicles every day, most of them from the Ile-de-France region that includes Paris.

Socialist mayor Anne Hidalgo's plans have prompted an outcry from the conservative-controlled Ile-de-France regional government.

Responding to fears that the new measures would worsen the peripherique's traffic jams, Belliard said that "we want to get the same number of journeys done with fewer vehicles".

"The peripherique should no longer be an urban motorway" but an "urban boulevard", he added.

The peripherique has already seen reductions in its speed limit since it was completed in 1973, from 90 kph to 80 in 1993, then to 70 from 2014.

Drivers are alone in some 80 percent of the cars on the ring road.

After the Olympics, the left-hand lane will be reserved for cars carrying two or more people during peak times, with cameras used to fine infringers.

But there was one bone thrown to road users, as motorbikes and scooters will be legally allowed to wend between the often-jammed lanes -- as many already do.