Reacción a "If cities imitated Copenhagen's cycle network, vehicle emissions would fall by 6%"

This study represents a significant milestone in global research on active transport. Its main strength lies in the use of the Google Environmental Insights Explorer (EIE) dataset, which for the first time allows for a methodologically consistent analysis of walking and cycling transport rates in more than 11,500 cities in 121 countries, covering 41% of the global urban population. From a scientific perspective, it is a methodologically rigorous study, transparent about causality limitations and with results supported by sensitivity analyses. The use of a Bayesian hierarchical model allows for the capture of both local (city) and national effects, integrating variables such as urban density, cycling infrastructure, topography, climate, fuel prices and GDP per capita.

The work is in line with the growing interest in promoting sustainable cities and provides new global evidence by demonstrating that urban density and street design positively influence active transport, even beyond traditional European cities, where this association has already been widely studied. However, the study has a number of limitations that should be noted. The first of these is the absence of individual-level socioeconomic data. This limits our understanding of how the effect of the environment varies depending on the effects of population inequality (income, gender, age, etc.). Furthermore, the aggregation of data at city level makes it difficult to capture intra-urban or seasonal dynamics. EIE data are not representative in countries with low smartphone access, which limits their validity in socially disadvantaged environments. The associations studied have no causal implication, a fact acknowledged by the authors themselves, which is a normal limitation of studies with such a broad global scope. Finally, associated with the characteristics of the data, a limitation of the study is the use of the length of cycle paths as the only proxy for urban design for its use, which oversimplifies the complexity of the urban environment.