An unusually long period of stable weather with little rain or wind has driven air pollution levels to record highs in Italy and prompted emergency measures in a number of cities.

That has happened before, especially in Milan, which is in a valley and is prone to weather conditions that trap air pollution close to the ground. Even so, the city government's decision on Wednesday to restrict traffic between 10 a.m. and 4 p.m. for three days next week made headlines and raised health concerns.

In Rome, the special commissioner who is acting as mayor said Thursday that car traffic in the city would once again be limited next Monday and Tuesday in the early morning and late afternoon, based on the last digits of license plate numbers, while single-ride tickets on the city's transit system would become passes valid all day. The city has resorted to similar steps several times this fall, including Monday and Tuesday this week. Violators face a fine of about $165.

The weather has been unusually mild and dry. Many regions have had no rain for more than seven weeks, and none is forecast until early January. As a result, in Rome, "high concentrations of particulate matter and nitrogen dioxide continue, aggravated by the weather situation of high pressure and absence of wind," the city government said.

Many cities across Italy faced similar problems. In the northwestern city of Turin, public transportation was free for two days this month to encourage commuters to leave their cars at home.

When levels of dangerous particulate matter in Milan's air rose above European Union pollution limits in November, the city put limits on diesel cars, which are generally more polluting than gasoline-fueled models.

The city also made bus and tram rides free for families taking their children to school, and began allowing passengers unlimited travel on public transit for about $1.65 a day, which officials said had increased ticket sales by 11 percent.

The mayor of Milan, Giuliano Pisapia, urged mayors of neighboring towns to join in his city's action because the pollution problem was affecting the whole region.

"For these provisions against air pollution to be more effective, they have to regard a vast area, and not only the individual towns," Mr. Pisapia said in a statement.

Scientists say that such an extended period of high atmospheric pressure is an unusual phenomenon for the Mediterranean in autumn and winter. But many argue that whatever the weather, Italy needs to get better control over the heavy traffic choking its cities and the emissions from home heating systems that are scarcely monitored by the authorities.

"Blocking traffic for one or two days is merely a palliative; so is stopping cars based on license plate numbers," said Nicola Pirrone, director of the Institute of Atmospheric Pollution Research at Italy's National Research Council. "Italy needs serious infrastructural investments to enhance greener transportation and greenhouse emissions."