Source: Wikipedia.
Mumbai is the largest city in the world served by a single runway. The city’s Chhatrapati Shivaji International Airport (CSIA) has two intersecting runways, but only one is used at any given time, leading to frequent congestion. By comparison, the main international airport serving the similar-sized city of Cairo has three parallel runways. With no room to expand CSIA, the Indian government is building a new secondary airport for Mumbai (Dinkar Balu Patil International Airport) with a targeted opening date of 2024, though the project has been beset by frequent delays.