US airline system traffic in August remained unchanged from a year ago after inching down in a month earlier, the US Transportation Department reported on Wednesday. US airlines carried 66.3 million domestic and international passengers in August 2012, unchanged from the same period of 2011, said the department. But the fresh number of passengers was still 0.1 percent above that of two years ago in August 2010. Specifically, there were 0.2 percent fewer domestic passengers and 1.1 percent more international passengers in August than a year ago. Southwest Airlines following its merger with AirTran carried more total system and domestic passengers than any other US airlines in August, reaching 12.024 million and 11.891 million, respectively. United Airlines took the first place in terms of international passengers with as many as 2.3581 million. In the first eight months of this year, US airlines carried 499.3 million passengers in total, up 1.0 percent from the same period in 2011. Domestically, the airlines carried 434.1 million passengers, while they carried 65.3 million international passengers. Suffering from economic crisis, the US airline industry experienced sharp decline in flight demand. However, the nation's airline traffic has been gradually peaking up from the early 2010.