Many fast growing cities have designated greenbelts but have failed to maintain them. This is often attributed to weak planning regulations, but there is little understanding of the underlying impacts of greenbelts on the interactions among land use control, transport supply and economic activities. This paper presents a counterfactual analytical model to examine the greenbelts' impacts on consumers' utility, producers' productivity, and their locational choices. The model establishes historic-what-if scenarios and compares what historically happened with what could have happened under alternative levels of greenbelt interventions. The model is applied to Beijing, which intended to establish two greenbelts in 1994, but large parts of the greenbelts have disappeared under fast urban expansion. The model compares the economic impacts of the greenbelts as they stood with hypothetical fully-enforced greenbelts and no-greenbelt scenarios from 1990 to 2010. The modelling results show that the two greenbelts, if fully enforced, would have decreased consumer surplus by $202 million in Beijing in 2010. To fulfil the policy aim of decentralisation, transport improvements between the city and new towns are crucial. For a more effective implementation of greenbelts in the future, development constraints could be carefully removed from non-ecologically sensitive sites which are served with good transport conditions.

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Greenspaces at the city scale, like greenbelts, green-wedges or green-grids have become wellknown instruments for shaping urban economic activity and land use. The economic impacts of such instruments are complex and hard to measure. This paper addresses one of the rarely studied problems of measuring economic impacts of alternative greenspace configurations in fast growing cities. In such cities, there is an uncertain basis for making such greenspace related decisions, for example the assumptions about the cities' total population and economic activity. Decision makers have few tools to measure and predict the potential economic costs and benefits of alternative greenspace configurations. We present a new model that allows tracking over time of both non-divisible land use decisions and a multitude of gradual adaptations made by businesses and consumers. The model is applied to Greater Beijing, one of the fast growing cities that is actively exploring alternative greenspace configurations to control urban expansion. The modelling results suggest that compared to the trend-development scenario of no greenspace intervention, a strict greenbelt would decrease the overall consumer surplus in Beijing by $3.3 billion, while an adaptive mix of green-wedges and green-grid would increase consumer surplus by $3.6 billion per year in 2030. The adaptive configuration also reduces car journeys by 11% in Beijing. More generally, modelling results show that a flexible design of strategic greenspaces and careful siting of new development around metro stations within the designated greenspaces could benefit consumers and promote sustainable travel.

Abstract:The growth of the main built-up area of Beijing is characterised by a pancake like expansion, from 100 km 2 in 1950 to 1210 km 2 in 2005 in successive waves. The approach to future urban expansion will require careful consideration, as economic, environmental and social conflicts at the urban fringe have intensified. Two successive greenbelts have been designated to contain expansion and engender more compact growth. However, the first greenbelt has not been achieved successfully and many areas designated as the second greenbelt is facing implementation challenges. This paper builds on existing research into greenbelt policy implementation and investigates the impacts of alternative urban growth boundary proposals under a systematic modelling framework. It reviews the theoretical insights into growth at the urban fringe, and puts forward a methodology that links development at the urban fringe to the functioning of the entire metropolitan area. It outlines six alternative development scenarios that encompass the existing planning proposals for the urban fringe: trend growth, densification, stringent greenbelt, loose greenbelt, hybrid controls, and green wedges. We use a prototypical spatial equilibrium model to quantify the performance of the development scenarios in terms of production costs, consumer welfare, wages, floorspace rents, and commuting times. The analyses suggest that the physical forms of fringe area development do significantly affect the economic performance of the whole municipality. Alternative proposals, including those that have rarely considered in the past, should be investigated carefully in this light, in conjunction with related studies on social and environmental impacts of urban fringe development.

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