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Don't bother calling your supplier in China in about a week. There is a good chance he will be closed for the Lunar New Year -- and most of his staff will be packed onto trains heading back to their hometowns.

You think traffic is tough around Thanksgiving? Try getting stuck among the 156 million Chinese taking trains around the weeklong Lunar New Year holiday, which this year starts on February 18.

Every year, there is a flood of humanity around the Lunar New Year as migrant workers in the cities -- who labor in the factories, construction and service industries that are powering China's astonishing growth -- scramble to find a way home. On top of all the rail passengers, the government estimates that 2 billion trips are taken by road around the weeklong holiday.

This huge annual migration offers an insight into many of the strengths, weaknesses and worries that underlie China's transformation into a global economic superpower. One change: The government isn't raising rail-ticket prices as it usually does around the holiday period, in part because of complaints about price gouging and a growing recognition of the hardships the migrants face.

The vast majority of migrants going home will be packing China's trains in journeys that can easily last two days. After years of neglect, the Chinese government is spending billions of dollars on improving rail lines and is promising more comfortable and faster trips on new bullet trains. Beijing intends to spend 1.25 trillion yuan, or about $160 billion, between now and 2010.

The riders may have Hao Jinsong to thank for the decision not to raise ticket prices. A graduate student at the China University of Politics and Laws, Mr. Hao sued the Ministry of Railways to get it to stop raising ticket prices during the holiday rush. He claimed that prices were raised without the required public hearing, but he also sought to show that people could use the court system to seek redress. "We needed a test case. We found a target and then went for it," Mr. Hao said.

The problem of prices is particularly acute for the migrants who depend on trains, which are a cheaper alternative to buses and planes, whose ticket prices are simply unattainable for many people. The salaries of construction workers are sometimes withheld by foremen who fear they won't come back after the holiday. This year, the government organized a special train to carry home 1,200 people who work on Olympics projects in Beijing.

All that mass movement leaves a big gap in what has become the world's factory floor. The Taiwan technology companies that are some of the biggest manufacturers in China say they either scale down or suspend their operations during the holiday week. Quanta Computer Inc., one of the world's biggest makers of laptop computers, and Asustek Computer Inc., one of the biggest makers of computer motherboards, both say they shut down their manufacturing operations during the holiday. Delta Electronics Inc., which makes electric-power supplies, says it only operates about 30% of its production capacity in China during the holiday.

Once these workers get home, they can look forward to the traditional Lunar New Year treat of pork dumplings -- especially appropriate to celebrate the start of the Year of the Pig.