Do higher urban densities contribute to more sustainable cities and communities? This paper examines the effectiveness of higher density (as a means) for achieving sustainable urban development (the goal) following three lines of enquiry. First, a systematic review of the scientific literature (n = 229 peer-reviewed empirical studies) is presented on the effects of urban density. Second, the motivations for increasing urban density are studied in a systematic review of Swedish planning practices based on the comprehensive urban plans in 59 municipalities. Third, these two studies are compared to find matches and mismatches between evidence and practice. Although positive effects exist for public infrastructure, transport and economics, there are also considerable negative environmental, social and health impacts. This creates a challenging task for urban planners to assess the trade-offs involving densification and accommodate current urbanisation rates. Some topics are found to be over-represented in research (transport effects), seldom discussed in practice (environmental impact), and misaligned when comparing motives and evidence (social impact). Furthermore, for some topics, urban density thresholds are found that are important because they may explain some of the divergences in the results between studies. PRACTICE RELEVANCEThe transfer of knowledge from research to planning practice is a serious concern as planning strategies are not aligned with scientific evidence. Planning practice in Sweden is more positive about the contribution of higher density to sustainable urban development than the results of empirical studies warrant. The largest deviation is found in relation to the social impacts of higher density where the planning arguments are not aligned with the evidence. Several reported negative effects of densification (e.g. water management, recreational infrastructure, biodiversity) are not sufficiently accounted for in Sweden's

One of the current dominant strategies proposed for sustainable urban development is densification. While some advocate the very reasonable benefits of density, others emphasize the potential drawbacks. The main goal of this paper is to provide a systematic overview of the claimed benefits of densification in Swedish practice and relate this to the scientific evidence. For the systematic overview, comprehensive plans from 59 Swedish municipalities, covering plans from both highly urbanized areas as well as more rural regions, are included. The results show that in three out of four cases where density or densification is mentioned, no motive is given. For the other quarter, the most often used motivation is related to transport (19%), services (17%) and urban environmental qualities (14%). The least frequent motives used are related to health (8%) and ecology (2%). The motives in comprehensive plans are for the most part pointing to a positive impact of density on sustainable urban development (77%), which is not always supported by the empirical evidence that more often describe a negative correlation. Furthermore, many of the most frequently used motives in comprehensive plans have little scientific support, which puts new questions on the research agenda.