Among European cities of its size, the German town of Freiburg has acquired an unusual reputation. Journalists write about it as a laboratory for sustainable urban living, planners visit it in organised tours, and its residents are regularly surveyed about habits that, elsewhere, would be considered unremarkable. The interest is not accidental. Over the past four decades Freiburg has made a series of decisions that, taken together, have reshaped the relationship between the city, its transport, and its energy supply. What makes the case particularly instructive is that none of those decisions was, in isolation, especially radical.

Freiburg's trajectory began in the 1970s, when the regional government announced plans to build a nuclear power station at the nearby village of Wyhl. Local farmers, already uneasy about the effect on vineyards, were joined by students from the city's ancient university. The resulting protest movement, unusually broad for the period, eventually forced the plant to be cancelled in 1975. The aftermath matters more than the protest itself. Many of the groups formed during the Wyhl campaign did not disband; they turned their attention to questions of how the city might manage without such a plant, and how its own demand for energy might be reduced.

Transport came first. In 1972, Freiburg had begun to preserve rather than dismantle its old tramway, at a time when most West German cities were ripping up tracks in favour of buses. The trams were gradually extended, fares were kept low, and from 1984 a single monthly ticket gave access to the whole regional public transport network. The ticket was the first of its kind in Germany and proved strikingly popular: within five years, public transport journeys per resident had risen by roughly a third. Ridership has continued to grow, while car use has fallen in absolute terms, a combination that planners elsewhere have found very hard to achieve.

Housing changed more slowly but more visibly. The district of Vauban, laid out on a former French military base during the 1990s, was conceived from the outset as a car-light neighbourhood. Only certain streets are open to through traffic, residents who do not keep a car pay a reduced service charge, and most dwellings are built to the low-energy 'passive house' standard, which drastically reduces the need for heating. A separate district, Rieselfeld, applied similar principles on a larger scale. Architect Dr. Petra Vollmer, who consulted on both projects, has argued that the decisive element was not any single technology but the decision to design streets for pedestrians first. 'Once the walking is pleasant,' she writes, 'many other things become possible.'

Energy policy followed a different route. Freiburg sits in the sunniest part of Germany and, in the 1990s, began to invest in solar research. The Fraunhofer Institute for Solar Energy Systems, founded in the city in 1981, expanded rapidly, and solar panels became a visible feature of public buildings, including the main football stadium and the roof of the central railway station. By 2010 the city's installed solar capacity was the highest of any comparable German municipality. Solar electricity alone, however, was never likely to cover the city's needs. More important, in the view of energy researcher Simon Thaler, was the combined-heat-and-power plant at Landwasser, which uses the waste heat from electricity generation to warm thousands of homes through a district heating network.

The results are measurable. Per-capita carbon emissions in Freiburg are roughly 25 percent below the German national average, and the city has set a target of climate neutrality by 2038. Whether that target is reached will depend on decisions that lie beyond the municipality's control, particularly national policy on electricity generation and industrial manufacturing. But the direction of travel is clear. Thaler points out that none of the individual Freiburg policies is unique; what is unusual is that they were pursued consistently across several decades, by administrations of different political colours.

This consistency is the feature that outside planners often struggle to replicate. A new tram line or a solar roof is easy to copy; a political culture in which residents expect to be consulted about parking standards, and in which small neighbourhood associations regularly propose improvements, is harder to transplant. Dr. Vollmer warns visitors against treating Freiburg as a template. The lesson, she suggests, is not about any particular technology but about patience: the willingness to let small, sensible choices accumulate, rather than waiting for a single transformative project that may never arrive.