IN ANCIENT times, Beijing built towering city walls that helped to prevent undefendable sprawl. These days it builds ring roads, stretching built-up areas ever outwards. Near Langfang, a city halfway between the capital and its giant neighbour Tianjin, diggers dip their heads and cement mixers churn, paving the next circular expressway. When complete, the 900km (560-mile) Seventh Ring Road will surround Beijing at such a distance that most of it will run through the neighbouring province of Hebei, to which Langfang belongs, rather than the capital itself. Parts of it are 175km from Beijing’s centre (see map).

The Seventh Ring Road (really the sixth, but for obscure reasons there is no First Ring Road) is emblematic of modern Chinese cities: giant, sprawling and dominated by cars. Even before it is completed in a year or two (and its use assessed), another, even longer, orbital is being plotted. Like many of China’s infrastructure projects, the new road displays engineering prowess. The country’s successes in urban planning are less evident.

Breakneck urban growth has propelled China’s rise in the past three decades. Migration from the countryside has helped expand the urban population by 500m—the biggest movement of humanity the planet has seen in such a short time. Over half the population is now urban. Some live in the basements of apartment blocks, or in shacks built in courtyards. But Chinese cities have mostly avoided the squalor of many developing-world ones.

The result of this urban growth is not just that China has many large cities—more than 100 of them have more than a million people—but that some are supersized. At the end of last year the government at last acknowledged the special nature of these, introducing the term “megacity” to describe those whose populations, including that of their satellite towns, exceed 10m. Of the 30 cities worldwide that match this definition, six are in China: Shanghai (23m), Beijing (19.5m), Chongqing (13m), Guangzhou (12m), Shenzhen (11m) and Tianjin (11m). A further ten Chinese cities contain 5m-10m people. At least one of these, Wuhan, will pass 10m within a decade.

China depends on its cities for economic growth and innovation. But it is failing to make the most of its largest conurbations. Medium-sized agglomerations of 1.5m-6.5m are outperforming bigger ones in terms of environmental protection, economic development, efficient use of resources and the provision of welfare, says McKinsey, a consultancy. Residents are beginning to question whether their quality of life, which for many has improved by leaps and bounds, will continue to do so. The giant cities are polluted, pricey and congested. Average travel speed in Beijing is half that in New York or Singapore.

Most of China’s cities share the legacy of a central-planning mindset in which all life and work was centred on a single “work unit”. Cities were “built as producer centres rather than consumer ones”, says Tom Miller, author of “China’s Urban Billion”. Their planning focus was on industry; not commerce, services or even community. The work units are gone but the tradition of dehumanising architecture persists. Most new developments are built on giant blocks 400-800 metres long.

China has swapped its socialist dream for an American-style one of cars and sprawling suburbs. The number of cars has increased more than tenfold in the past decade, to 64m. The combination of superblocks and car-lust often adds up to a giant jam. Large blocks mean fewer roads to disperse traffic. Guidelines require a main urban road every 500 metres and an eight-lane road every kilometre. In the case of Beijing, a ring and radial system was also created, with the aim of providing speedy road access in and out of town, bypassing city traffic and linking satellite towns. Not a bad idea, except that workplaces have remained concentrated in the centre. The expressways funnel traffic into gridlock.

The ill-defined ownership rights of farmers have encouraged the sprawl. Officials can expropriate rural land easily and at little cost. Doing so is far cheaper than redeveloping existing urban areas. Industrial land is heavily subsidised, so factories have remained in urban areas rather than move to cheaper sites on city outskirts. The amount of land classified as urban has more than doubled since 2000—40% of new urbanites became so when cities engulfed their villages.

Sprawl has resulted in populations becoming more thinly spread. China’s megacities are less dense than equivalents elsewhere in the world (see chart). Guangzhou could contain another 4m people if it was as packed as Seoul in South Korea; Shenzhen could be larger by 5m. Extending outward takes a toll: slow commutes from far-flung suburbs increase fuel consumption and cut productivity.

Massive spending on infrastructure has hugely improved connections within and between cities. Since 1992 China has spent 8.5% of its national income on infrastructure each year, far more than Europe and America (2.6%) or India (3.9%). Yet city residents still complain. Subways are often built as engineering projects, with stops at set distances, rather than where people want them to be, says Sean Chiao of Aecom, an infrastructure firm. Buses, metros and rail networks are poorly integrated because separate agencies manage them. Planners often ignore the needs of 200m or more residents who have no urban hukou, the household registration certificate that is needed for access to public services. Cities therefore have inadequate hospitals, schools and affordable housing. This year, however, the central government has started to downplay the importance of GDP growth in assessing the performance of local officials. That should free them to spend more money on making cities better places to live, rather than on laying concrete. Some cities now seek to limit car use. Beijing is mulling a congestion zone. To limit pollution and improve traffic flow, eight cities (including all megacities except Chongqing) cap the number of new licence-plates they issue. Several cities ban some drivers one day a week. Metro systems are fast multiplying: Beijing alone opened four new lines with 41 new stops in December. More could be done. Parking in city centres remains far too cheap, and laws should be enforced to curb a habit of parking on pavements or traffic islands. Buses could be made to use the central lanes of broad boulevards. Bicycle-use should be encouraged by reintroducing once ubiquitous cycle lanes.

The World Bank says that, at 54%, China’s degree of urbanisation is still well below the 70% expected of a country with its current income level per person. The flood of migrants will continue; by 2030 Chinese cities will contain more than 1 billion people. A change of thinking will be needed to make them better places to live in.