– Paris enjoyed a rare reprieve from traffic jams Monday as a draconian clampdown on cars took effect, aimed at banishing stubborn levels of smog.

Only cars and motorcycles with license numbers ending in an odd number were allowed on the streets of the French capital on Monday. Close to 4,000 motorists with plates ending in an even number who slipped behind the wheel had received on-the-spot $30 fines by midday.

The measure was announced by the national government over the weekend as a way of trying to lift the cloud of particle pollution that has hung over the city for the past week, cloaking the Eiffel Tower and other monuments in a gray sheen.

Many motorists had complained about the restriction, but significantly reduced rush-hour traffic pointed to high levels of compliance.

Transport Minister Frederic Cuvillier said morning traffic jams had shrunk by 60 percent as affected motorists opted to car pool or take public transportation.

Electric and hybrid vehicles, taxis, ambulances, driving school cars, refrigerated trucks and vehicles with at least three passengers were exempted from the measure.

The government had toyed with continuing the ban Tuesday, with a switch to even-number-only plates.

But with forecasts pointing to a significant improvement in air quality from Tuesday, the continuation was deemed unnecessary, Environment Minister Philippe Martin told a news conference.

A spate of warm, windless spring weather, coupled with cold nights, has been blamed for trapping the pollution that has cast a pallor over most of northern France and parts of the southeast in the past week.

Pollution levels in Paris remained at dangerously high levels over five consecutive days last week. The cities of Lyon, Caen, Rouen and Grenoble were among other locations affected.

The last time France grounded cars over pollution was in 1997.