6 OCTOBER CITY, Egypt  The highway west out of Cairo used to promise relief from the city’s chaos. Past the great pyramids of Giza and a final spasm of traffic, the open desert beckoned, 100 barren miles to the northwest to reach the Mediterranean.

That, at least, was the case until recently. Now, the microbus drivers and commuters driving from Cairo cross 20 miles of nothingness to encounter a new city suddenly springing from the sand. A distressingly familiar jam of cars and a cluster of soaring high-rises herald the metropolis that is designed to relieve pressure on the historic center of Cairo, which city planners have deemed overtaxed beyond repair.

Welcome to the new Cairo, not entirely different from the old one.

Cairo has become so crowded, congested and polluted that the Egyptian government has undertaken a construction project that might have given the Pharaohs pause: building two megacities outside Cairo from scratch. By 2020, planners expect the new satellite cities to house at least a quarter of Cairo’s 20 million residents and many of the government agencies that now have headquarters in the city.

Only a country with a seemingly endless supply of open desert land  and an authoritarian government free to ignore public opinion  could contemplate such a gargantuan undertaking. The government already has moved a few thousand of the city’s poorest residents against their will from illegal slums in central Cairo to housing projects on the periphery.