Changes to the busy Beijing-Kunming air route have increased the maximum number of planes that can travel between the two cities by 40 per cent, a move that may be repeated throughout the country to reduce flight delays. The Civil Aviation Administration of China (CAAC) said the modified route, which separates north and southbound flight paths laterally instead of vertically, would cut air traffic congestion for 54 cities along the corridor, including Chongqing , Chengdu and Xian . The air route is one of the busiest on the mainland, handling 1,100 flights daily. The CAAC's Air Traffic Management Bureau is considering optimising nine more busy air routes, including those linking Beijing and Shanghai, Beijing and Guangzhou and Shanghai and Harbin, bureau official Zhu Xiaoying told China National Radio. Zhu did not provide a timetable, saying optimising air routes was a complicated process that involved many considerations. The public has complained for years about frequent and lengthy delays at airports, some of which are among the world's worst for on-time departures and arrivals. In the first half of this year, only 18 per cent of flights departed Beijing on time. In Shanghai the rate was 28 per cent. There have been many reports in recent years of angry passengers attacking airport and airline staff after prolonged delays, which puts additional strain on management and security. The government has ordered airlines and airports to address the issue. Aside from separating flights travelling in opposite directions, the CAAC has adjusted a few existing airways and added some new segments. The changes should help settle conflicts stemming from limited capacity and rising air traffic, said Zhang Lu , an engineer with the Northwest Air Traffic Bureau. "It's like expanding a country road - where cars drive on both sides - into a highway, so that drivers do not need to worry about the traffic on the other side," Zhang said. The move would cut in half the risk of accidents along the Beijing-Kunming route and make work easier for air traffic control staff, the CAAC said. Cutting flight delays should also cut airlines' operating costs.