Each day, Cairo's streets are densely packed with cars, crowded buses and numerous other forms of transportation. The bustling traffic has affected the city's air quality—and limited people's access to commercial and industrial centers.

Egypt's National Authority for Tunnels worked with PB to offer one solution: Line 2 of the Greater Cairo Metro, a state-of-the-art, three-line transit system that cuts underneath the ancient city to link its inhabitants more closely together.

The system's Line 1, which began revenue operations in 1989, created a new underground section to connect two pre-existing railways. PB led the joint venture to design and construct Line 2—which includes the first-ever crossing under the Nile River—adding 19 kilometers (12 miles) of two-track heavy rail service and 18 stations to the Metro system.

In highly populated areas, underground construction presented an enormous challenge. But thanks to teamwork, cooperation and innovative technology, this project's historic new line was completed in October 2000.