Infrastructure projects undergo multiple changes throughout their lifecycle, adapting to new mobilities, technologies and environments. We build on the System of Systems (SoS) theoretical concept to understand the implications of such infrastructure transformations, specifically when projects move from a single purpose to hosting multiple functions. Using multiple case studies in Europe, we investigate which functions will likely be added to the original infrastructure and the rationale for adding these functions. Therefore, we expand upon the theoretical concepts of circularity, resilience, and social sustainability, wherein multifunctional infrastructure adapts, renews, and complements existing infrastructure.

Air pollution remains a major environmental and health concern in urban environments, especially in street canyons that show increased pollution levels due to a lack of natural ventilation. Previous studies have investigated the relationship between street canyon morphology and in-canyon pollution levels. However, these studies are typically limited to the scale of a single street canyon and city-wide assessments on this matter are scarce. In 2018, NO₂ concentrations were measured in 321 street canyons in the city of Antwerp (Belgium) as part of the large-scale citizen-science project “CurieuzeNeuzen”. In our research, this data was used to study the correlation between morphological indices (e.g. aspect ratio (AR), lateral aspect ratio (LAR), presence of trees) and the traffic volumes on a city-wide scale. The maximum hourly traffic volume (TV_max) and AR correlated significantly with the measured NO₂ values, making them useful indicators for air quality in street canyons. For street canyons with AR > 0.65, a TV_max of 300 vehicles/hour was found as a threshold value to guarantee acceptable air quality. No significant correlations were found for the other parameters. Finally, a number of typical street canyon types were defined, which can be of fundamental interest for further research and spatial policy making.

After a decade marked by the renewal of grand European high-speed railway stations, today, a second wave of station renewal is at hand. This paper argues the importance of the train station in the historical development of smaller cities. Based on comparative research of recent best practices, the contemporary urban design challenges of smaller and medium-sized stations are explored. The paper concludes that the station is no longer shaped as a monolithic, architectural cathedral, as for the grand stations, but interweaves the world of the passer-by with that of the local inhabitant as a system of public infrastructure and facilities.