As urban populations continue to swell and environmental concerns mount, understanding how transportation infrastructure impacts urban mobility patterns is more critical than ever. Despite the widely recognized disadvantages of car ownership—including congestion, pollution, and urban sprawl—global trends still indicate a consistent rise in private vehicle use. This ongoing reliance on automobiles underscores the urgent need to promote viable alternatives such as active mobility and public transportation. However, the effectiveness of public transport options varies significantly, a factor that is crucial for urban planners and policymakers striving to reduce car dependency. A groundbreaking study recently published in Nature Cities delves deeply into this topic, offering a data-driven comparison of modal shares in European cities featuring different types of rail systems.

The study, authored by Ricardo Prieto-Curiel, leverages an extensive dataset curated by CitiesMoving.com, a comprehensive platform that harmonizes mobility surveys from cities worldwide according to the ABC framework. This framework classifies journeys into three key categories: active mobility (A), which includes walking and cycling; bus and other forms of public transport (B); and private car use (C). By examining modal shares across various European locales, the research distinguishes between cities equipped with metro systems, tram-only cities, and those lacking any rail infrastructure. The findings present a nuanced narrative about how these different transportation frameworks influence urban travel behavior—particularly the extent to which they succeed in mitigating car use.

One of the study’s pivotal insights is the marked difference in car usage between cities possessing metro systems and those with only tram networks or none at all. Metro-equipped cities demonstrate a considerably lower share of journeys made by car. Such a trend suggests that rapid transit systems, with their capacity for high-frequency, long-distance travel, more effectively dissuade private vehicle use compared to trams, which often have lower capacities and shorter ranges. This observation not only challenges common perceptions that all rail transit equally curbs car dependency but also underscores the unique role of metro systems within the urban transport ecosystem.

The distinction between metros and trams lies not only in their physical infrastructure but also in their operational frameworks and network integration. Metros typically run on dedicated tracks, separated physically from other traffic, ensuring consistent speeds and reliability. Their ability to cover greater distances without frequent stops and their incorporation into larger multimodal networks make them a dominant choice for commuters traveling longer distances within metropolitan areas. In contrast, trams often share road space with other vehicles, which can subject them to delays caused by traffic congestion. Their shorter routes and more frequent stops make them better suited for localized travel, potentially limiting their effectiveness in replacing car trips.

Cost and accessibility factors are also instrumental in explaining why metro systems significantly reduce car journeys while trams do not show the same impact. Construction and operational expenses for metros are considerably higher, confining their presence to economically robust cities or those with large population densities justifying such investment. This exclusivity might mean that residents in metro cities have fewer viable alternatives to private cars, making the metro’s efficient service a more attractive option. Tram systems, though generally less costly to deploy and maintain, primarily serve smaller urban areas or act as feeders to other transit modes, which may diminish their overall influence on curtailing car use.

The health, economic, and environmental benefits of active mobility and public transportation are well-documented, rendering the insights of this study particularly salient. Cities are increasingly championing policies designed to encourage walking, cycling, and the use of public transit to mitigate the environmental footprint of urban travel. Yet, this research provides a sobering reminder that not all public transport solutions yield equal returns in these efforts. Policymakers must therefore evaluate the specific context of their cities, considering whether investments in metro infrastructure might yield more substantial reductions in automobile dependency than expansions of tram networks or other forms of public transit.

Moreover, the study’s utilization of the ABC framework adds a layer of sophistication by allowing analysts to harmonize data across diverse cities and compare transport modes on a standardized basis. This methodological approach addresses the common challenge of inconsistent data collection methodologies that has often hindered cross-city comparisons in mobility research. By categorizing journeys via active mobility, bus/public transport, and private cars, the framework provides a clear lens through which the complex interplay of urban transport modes can be understood, facilitating actionable insights.

Another noteworthy aspect of the study is the geographic focus on European cities. Europe’s extensive diversity in urban morphology, economic development, and transport infrastructure offers fertile ground for such comparative analyses. From sprawling metropolises with advanced metro networks to smaller cities relying primarily on trams or buses, the continent embodies a spectrum of structural and cultural approaches to urban mobility. The research findings thus carry important implications beyond Europe, shedding light on transit planning strategies that could be applicable to emerging cities worldwide grappling with similar challenges.

Environmental imperatives add urgency to these transportation debates. Private vehicles are among the largest contributors to urban air pollution and greenhouse gas emissions, exacerbating climate change and harming public health. The capability of metro systems to lower car usage directly translates to decreased emissions, less noise pollution, and improved air quality. By illustrating this link empirically, the study galvanizes support for the expansion of metro infrastructure as an integral component of green urban policy strategies. Conversely, the limited impact of trams on car reduction signals that tram investments, while beneficial for other aspects of urban transport, should be complemented by other initiatives to maximize environmental benefits.

The socio-economic dimensions of the study’s findings should not be overlooked. The reduction in car dependency facilitated by metro access often correlates with enhanced social equity. Metro systems typically serve a broad cross-section of urban residents, enabling affordable access to jobs, education, and amenities without the need for private vehicle ownership. This can alleviate economic burdens on low-income populations and increase overall urban inclusivity. The research thereby highlights a compelling social justice argument in favor of metro development, which aligns with broader goals of creating livable, equitable cities.

Technological advancements, such as real-time transit tracking, integrated fare systems, and electrification of fleets, further enhance the appeal and efficiency of metro networks. These innovations contribute to a seamless passenger experience that can draw travelers away from the convenience of private car use. While tram systems can also benefit from such technologies, their inherent operational constraints—like vulnerability to street-level conditions—may limit the extent to which these technologies can transform their effectiveness relative to metros.

The study also invites reflection on the future trajectories of urban transport amidst evolving lifestyles and work habits. The COVID-19 pandemic fundamentally altered commuting patterns, with increases in remote and hybrid work reducing overall transit ridership temporarily. However, as cities adapt to post-pandemic realities, the role of reliable, efficient public transport remains pivotal. Investing in metro systems can offer a resilient backbone for urban mobility, adapting dynamically to fluctuating demand while continuing to discourage excessive reliance on private vehicles.

Importantly, the findings challenge urban planners and policymakers to critically evaluate incremental improvements to tram systems versus transformative investments in metro expansions. While cost considerations often favor tram enhancements, these may not translate into meaningful reductions in car use without complementary policies such as congestion pricing, improved pedestrian infrastructure, and multimodal integration. A holistic approach that views metro development within a broader ecosystem of sustainable transport initiatives is essential.

In conclusion, the comparative analysis conducted by Prieto-Curiel provides compelling empirical evidence that metro systems hold a unique and potent capacity to reduce car dependency in European cities, outperforming trams and cities without rail systems. This revelation holds profound implications for urban mobility planning, environmental sustainability, and social equity. As cities worldwide face escalating pressures to decarbonize and improve quality of life, prioritizing the development and expansion of metro networks could be one of the most effective strategies to achieve these goals. This study, therefore, serves as a clarion call to rethink urban transport investments through the lens of impact, scalability, and long-term benefits.

Subject of Research: The study investigates the impact of different rail-based public transport systems—metros and trams—on private car usage and mobility patterns in European cities.

Article Title: Metros reduce car use in European cities but trams do not

Article References: Prieto-Curiel, R. Metros reduce car use in European cities but trams do not. Nat Cities (2025). https://doi.org/10.1038/s44284-025-00342-7

DOI: https://doi.org/10.1038/s44284-025-00342-7

Tags: active mobility promotionalternatives to car dependencycongestion and pollution reductiondata-driven mobility researchenvironmental concerns in transportationEuropean cities rail systemsimpact of transportation infrastructuremodal share comparisonpublic transportation effectivenesstram versus metro systemsurban mobility patternsurban planning and policy