Karaj

Karaj barely existed before Tehran needed a pressure valve. In the 1960s, this small town 40 kilometers west of Iran's capital had under 50,000 people. By the 2020s, the metropolitan area exceeds 3 million—a sixty-fold expansion in sixty years, driven entirely by Tehran's inability to contain its own growth.

The Karaj River dam (Amir Kabir Dam, completed 1961) created the city's water supply and its initial raison d'être: controlling floods and irrigating the agricultural plain between the Alborz Mountains and the central plateau. Tehran's explosive population growth—from 2 million in 1960 to over 9 million today—pushed lower-income residents westward along the highway to Karaj, where land was cheaper and apartments were affordable.

The result is a classic unplanned megacity. Karaj has the infrastructure of a small town and the population of a major metropolis. Traffic congestion on the Tehran-Karaj highway is among the worst in the Middle East, with hundreds of thousands commuting daily. Air pollution from both cities merges into a single toxic cloud trapped by the Alborz Mountains.

Karaj's economy is primarily residential and industrial. The city hosts manufacturing (automotive parts, food processing, plastics) that migrated from Tehran as land costs rose. Iran Khodro and SAIPA—Iran's two major automakers—have supplier networks extending into Karaj's industrial zones.

The Alborz province (of which Karaj is the capital, separated from Tehran province in 2010) struggles with the administrative challenges of governing a megacity that was never planned as one. Water scarcity is chronic: the Karaj River dam supplies both cities, and aquifer depletion threatens long-term habitability.

Karaj demonstrates what happens when a capital city's growth exceeds its boundaries without any corresponding plan: the overflow creates a shadow city that inherits all of the capital's problems and none of its resources.