Most proposals for car-free cities are heavy on idealism. Like high-tech products that sold easily to the few who understood them, but stalled when they tried to go mass-market, projects that create desirable living areas but are difficult to do business in are unlikely to be successful on a large scale.

By contrast, SkyTran offers "supply-side smart growth". It benefits suburbs and rural areas, to be sure, but it revolutionizes cities. It unleashes fundamental advantages of density that no suburban megalopolis or small town can match. Dense cities are likely to become the centers for high-value manufacturing and every kind of specialized profession -- technology, design, arts, or services.

The excitement and fast pace of today's urban lifestyles will go into overdrive with sophisticated services like ExtremeCustomization. Yet with most cars replaced, cities can also restore open space and beauty, or even incorporate human-scale villages . People are likely to move back into these kinds of cities in large numbers.

Once a city has many of the world's best chip designers or systems biologists or bankers or diamond cutters living and working in it, this concentration of talent makes it the best place to start or move more businesses and research centers for that industry. Personal contacts between the best and brightest in a field who go to school and then work and live and compete close together will speed up development and create even more pressure for the industry to concentrate there. SkyTran doesn't create this dynamic, but it allows it to proceed much further. Silicon Valley in California is probably still the world center of silicon chip design, but not much chip manufacturing goes on there today. An impossible housing market created by suburban zoning restrictions strangled manufacturing, with ordinary houses costing millions and ordinary people driving many hours each day to work there.

We expect that the results of this unleashing will be everything Smart Growth dreams of today -- plummeting resource consumption, efficient public services, and reduced environmental burden as growth concentrates in cities instead of sprawling out. Yet because the phenomenon will be driven by economics and personal interest as well as long-term social altruism, it will be far easier to sell politically and far more likely to change how the majority of people live.