The Yangtze River Maritime Safety Administration started the global position system (GPS) to monitor 107 passenger ships sailing in the Three Gorges enveloped by a dense fog. It ordered the ships to stop and wait by sending short text messages after the fog became too dense for sailing. Since China's Spring Festival travel season started three days ago, 50,000 passengers have safely traveled in and out of the Three Gorges. The upper reaches of Yangtze River, China's longest, have been hit by extreme dense fogs recently. As a measure of preventing sailing accidents, maritime authorities equipped passenger ships in the river with GPS facilities free of charge. Knowing the location of each ship, the authorities can easily monitor and manage the sailing in the river.