Budapest  - Thousands of motorists chose to ignore an order to stay of the roads on Monday, the first working day since Budapest issued a full scale smog alert that should have cut traffic by half.

The smog alert was issued on Sunday morning, bringing into effect Budapest City Council regulations passed in December that ban half of cars from the roads.

While an alert is in force on a odd numbered date, only cars with an odd registration number can drive in Budapest. On an even numbered day, only even numbered cars can drive in the city. That, at least, is the theory.

In practice, many drivers ignored the regulation, despite Prime Minister Ferenc Gyurcsany setting a good example by taking the tram to work.

Monitors appointed by the city council found that of 2,000 cars counted on one busy road, 1,300 were even numbered, and 700 were odd.

This suggests that over half of the owners of odd-numbered cars chose to ignore the smog alert and take to the roads anyway.

"Traffic is at the usual January level in the capital this Monday morning," said Marta Vizeli of the traffic monitoring service Fovinform.

A spokesman for Budapest Public Transport told the local news agency MTI that there was no significant rise in passenger numbers on Monday.

However, police spokeswoman Eva Tafferner said that traffic levels were lower than usual, comparable to a busy weekend day.

The police only had the power to inform drivers of the ban, not to penalise them for failing to observe it. Hungarian traffic regulations had not been modified to accommodate the city council regulations introduced in December.

"So we have this ridiculous situation where a smog alert issued on the basis of a City Council ruling, through the fault of the government, cannot be implemented," said the MP Zoltan Hock of the opposition Hungarian Democratic Forum.

An initial public warning was issued on Sunday morning after 24- hour average levels of airborne PM10 particulate matter - microscopic dust that forms smog and causes respiratory problems - stayed above 100 micrograms per cubic metre for a second day running.

Smog levels were high in towns across Hungary after several days of freezing, windless weather, only a few saw pollution levels comparable to that of the capital.

Air pollution was exacerbated by power stations switching from gas to oil power amid shortages due to the Ukraine-Russia row of pricing.

"It is very likely that the smog alert will be lifted on Tuesday morning," said Budapest City Council spokesman Krisztian Nyary as pollution levels fell on Monday evening. (dpa)