Cars will come off the roads. Factories will close. Construction will stop.
And persistent pollution might still hang over Beijing, enough to sour the Summer Olympics that begin next month.
Less than 40 days until the Opening Ceremony, an estimated 600 U.S. Olympians are devising plans to combat pollution as Beijing officials scramble to turn gray haze into blue skies and 550,000 foreign visitors hope for the best.
Some Americans won't arrive in the Chinese capital until a few days before they compete. Others will wear masks designed at the Olympic Training Center in Colorado Springs or use asthma inhalers under International Olympic Committee exemptions.
Athletes in outdoor endurance events lasting more than an hour, such as cycling, marathon and triathlon, face the prospect of delays in competition if air quality is poor, according to IOC president Jacques Rogge.
"The key is preparing them for the high level of interest," said Steve Roush, chief of sport performance of the Colorado Springs-based USOC. "Letting them know they need to stay focused and keep their mind set on what they need to do to perform on the field of play."
China contains 16 of the world's 20 most polluted cities by World Bank Web site estimates, hampered by vehicle emissions, dust from construction sites and soot particles from factory smokestacks.
China challenges the U.S. as the world's largest emitter of greenhouse gases and Beijing rivals Mexico City as the world's most polluted city. Pollution levels in Beijing are five times over the safety benchmark of the World Health Organization.
Half of the 3.3 million private cars in Beijing will be banned during the 17-day Olympics. More subway lines have been built and millions of trees have been planted between the Gobi Desert and Beijing to curb pollution.
Plus, 153 gas stations and oil depots will cease operations, more than 1,000 coal mines will shut down, construction will halt throughout the city of 17.4 million and hybrid-electric buses will serve Olympic venues.
"The health of the athletes is absolutely not in any danger," Rogge told The Associated Press. "It might be that some will have to have a slightly reduced performance. But nothing will harm the health of the athletes."
The USOC isn't leaving anything to chance.
Swimmers will train in Singapore before the Olympics, triathletes will practice in South Korea and canoe and kayak athletes will travel to Japan. Three-time world champion sprinter Tyson Gay is expected to prepare in Hong Kong.
Triathletes Matt Reed of Boulder and Jarrod Shoemaker hope to sport masks that cover their noses and mouths when practicing but not when competing. The masks include an activated carbon filtration system, eliminating most pollutants.
"Never have I felt my performance or the team's performance was affected by the pollution," said soccer player Heather O'Reilly, who has been to China six times. "We're confident in our team. We're going to focus on the things we can control."
O'Reilly's coach, Pia Sundhage, dismissed the pollution, saying, "The two teams have the same air to breathe. It's the same problem for both teams."
Marathon runner Deena Kastor pointed to pollution concerns heading into the 2004 Athens Games that vanished once the Olympics started.
"The conditions weren't as bad as we thought," she said. "The best three people are going to be the three people on the awards stand, regardless of what the conditions are presenting."