PARIS -- A new wave of departures by drivers starting their main summer holidays, plus the return of others, created a total of some 400 kilometers (250 miles) of snarl-ups on France's road network on Saturday, traffic officials said.

The National Traffic Information Center (CNIR) said the biggest jams were in the Rhone Valley of southeastern France, the main route for holidaymakers heading from Paris and other points north towards the Mediterranean.

Major jams were also reported on roads leading towards the Pyrenees and Spain.

The CNIR also reported high atmospheric pollution levels in the greater Paris region, due to the combination of warm weather and dense traffic.

Vehicles were ordered to keep their maximum speeds to 20 kilometers (12 miles) an hour less than the normal speed limits.

The great majority of French people take their annual holidays between the middle of July and the end of August, leading to massive road congestion on certain days of the year, AFP reported.