The Chinese are spending more time at airports and on aircraft as flight delays worsen.

The average delay for Chinese flights last year was 21 minutes, two minutes worse than in 2014, the Civil Aviation Administration of China said in a report dated May 30 on its website. Air traffic control issues was the biggest reason for the delays, followed by weather, according to CAAC.

Air China Ltd., China Eastern Airlines Corp. and other carriers are expanding their fleets and budget carriers have emerged as economic growth spurs travel demand in China, where the military dominates the country’s air space. Traffic congestion is set to worsen as the nation’s commercial aircraft fleet is projected to double in the next 20 years and become the world’s biggest travel market.

About 436.2 million people traveled by air in China last year, 11.3 percent more than a year earlier, according to the report.

Chinese airports fare poorly in timely airport departures, according to April data on Flightstats, a flight data site for consumers. Of the 49 airports it tracked, Shenzhen was ranked last, Guangzhou second-to-last, Shanghai’s two airports 45th and 46th, and Beijing 40th. Hong Kong placed 43. Istanbul was ranked the best, according to the website.

The world’s second-biggest economy plans to allocate about 77 billion yuan ($12 billion) for investment in civil aviation this year, starting with 11 key projects as it looks to improve infrastructure to cope with the surging travel demand.

China is planning to build 66 new civil airports during its next five-year plan, which will take the national total to 272 by 2020. Beijing, Chengdu, Qingdao, Xiamen and Dalian are among major Chinese cities that have started building new airports, while work began in December on two new passenger terminals at Shanghai’s Pudong International Airport.

©2016 Bloomberg L.P.

This article was written by Kyunghee Park from Bloomberg and was legally licensed through the NewsCred publisher network.

Photo Credit: A China Eastern 777-300ER aircraft. Boeing