Among the findings his office made was that settlements were often built on high ground, not only for defensive reasons but also to take advantage of the stronger winds. Some also used tall, hollow “wind towers” to funnel air down to street level. And the narrowness of the streets  which were almost always at an angle to the sun’s east-west trajectory, to maximize shade  accelerated airflow through the city.

With the help of environmental consultants, Mr. Foster’s team estimated that by combining such approaches, they could make Masdar feel as much as 70 degrees cooler. In so doing, they could more than halve the amount of electricity needed to run the city. Of the power that is used, 90 percent is expected to be solar, and the rest generated by incinerating waste (which produces far less carbon than piling it up in dumps). The city itself will be treated as a kind of continuing experiment, with researchers and engineers regularly analyzing its performance, fine-tuning as they go along.

But Mr. Foster’s most radical move was the way he dealt with one of the most vexing urban design challenges of the past century: what to do with the car. Not only did he close Masdar entirely to combustion-engine vehicles, he buried their replacement  his network of electric cars  underneath the city. Then, to further reinforce the purity of his vision, he located almost all of the heavy-duty service functions  a 54-acre photovoltaic field and incineration and water treatment plants  outside the city.

The result, Mr. Foster acknowledged, feels a bit like Disneyland. “Disneyland is attractive because all the service is below ground,” he said. “We do the same here  it is literally a walled city. Traditional cars are stopped at the edges.”

Driving from downtown Abu Dhabi, 20 miles away, you follow a narrow road past an oil refinery and through desolate patches of desert before reaching the blank concrete wall of Masdar and find the city looming overhead. (Mr. Foster plans to camouflage the periphery behind fountains and flora.) From there a road tunnels through the base to a garage just underneath the city’s edge.

Stepping out of this space into one of the “Personal Rapid Transit” stations brings to mind the sets designed by Harry Lange for “2001: A Space Odyssey.” You are in a large, dark hall facing a row of white, pod-shaped cars lined up in rectangular glass bays. (The cars’ design was based on Buckminster Fuller’s proposal for a compact urban vehicle, the D-45, which helps explain their softly contoured, timelessly futuristic silhouettes.) Daylight spills down a rough concrete wall behind them, hinting at the life above.