Air China planes are seen on the tarmac of the Beijing Capital International Airport. REUTERS/David Gray

The air above Beijing is about to get even more congested. China’s capital city is planning to build an airport worth $14 billion to serve the world’s second-busiest air hub.

Capital Airport, Beijing’s existing airport and China’s main gateway to the world, handled 83.7 million passengers last year, far exceeding its designed capacity of 76 million passengers per year, the Wall Street Journal reported on Tuesday.

The additional airport, slated to begin operation in 2018, will have a capacity rivaling the Capital Airport, with provisions for three additional runways as needed. It will be located about 29 miles south of the city center.

The number of air travelers through Beijing is set to nearly double that capacity – to 142 million passengers per year by 2020, a new environmental-impact report from China’s Ministry of Environmental Protection said, making the second airport all but necessary.

However, analysts are already questioning whether the new airport would be effective while China’s airspace remains as congested as it is now, the Wall Street Journal reported.

"It isn't uncommon for a metropolitan city to have two airports," said Edward Xu, a transport analyst at Morgan Stanley, adding that the second airport will not be fully utilized if airspace restrictions remain in place, leaving more than 80 percent of China’s airspace in military control. Just a handful of corridors and routes are open for civilian use, causing frequent delays for the country’s air travelers.

Currently, planes in the Capital Airport depart on average every two minutes, much longer than the 45-second intervals at London Heathrow Airport.