People drive significantly less in European cities with a metro system than in cities that only have trams or no rail-based public transport at all. This is shown by a new study from the Complexity Science Hub (CSH), published in Nature Cities.
[Vienna, November 7, 2025] — For his analysis, CSH researcher Rafael Prieto-Curiel examined mobility data from around 400 European cities. These data capture how daily commutes are distributed across three categories: active mobility (walking and cycling), public transport (metro, tram, bus), and (car, taxi, motorcycle, ride-hailing).
“I looked at 47 cities with a metro, 46 cities with a tram but no metro, and 285 cities without both,” explains Prieto-Curiel. The data come from a larger dataset he built for earlier work, available through the interactive visualization Cities Moving.
Share of Car Trips: 37% Versus 50%
In cities with a metro, the average share of car trips is 37%, compared to 50% in cities with trams only and 54% in cities without rail systems. “This means that, on average, people in cities without a metro make almost one and a half times as many car trips per capita as those in cities with a metro,” says Prieto-Curiel.
At the same time, residents of metro cities use public transport far more often (35%) than those in tram cities (21%) or cities without rail (16%).
The figures are weighted according to the population size of each city—“larger cities have a greater influence on the average because more people are on the move there,” Prieto-Curiel explains.
Commuting behaviour across 378 cities in Europe: Depending on whether cities have a metro system, only a tram network, or no rail-based network, the average commuting patterns, weighted by population, are shown on the left, across three mobility categories—active mobility (A), public transport (B), and motorized private transport (C). The triangular chart on the right shows the commute patterns of residents in all 378 cities. Each circle represents one city, with circle size indicating population and circle color indicating whether the city has a metro system, a tram network, or neither.
Larger Cities, Larger Effect
According to the study, the difference in mobility behavior grows with city size: In large cities with more than 750,000 inhabitants, the share of car commutes reaches 63% if there is no metro, regardless of whether a tram network exists. Meanwhile, the share of car trips in metro cities remains nearly unchanged at 36%. In other words: In cities with a metro, public transport use stays relatively stable as cities grow. In cities with only a tram, however, it declines as populations increase.
“There are naturally city-level deviations from this average,” Prieto-Curiel notes. “For example, Utrecht (Netherlands), Szeged (Hungary), and Bern (Switzerland) all lack metro systems but still have car shares of only around 20% thanks to high levels of active mobility. Conversely, Rome (Italy), despite having a metro, or Toulouse (France) with over 60%, both show relatively high car shares.”
“On average, however, there is a noticeable effect: Suppose a city has one million inhabitants. According to the calculations, about 370 million car trips per year occur if there is a metro. In a city of the same size with a tram but no metro, that number rises to 700 million, so almost twice as many.”
Small Changes with Big Impact: The Example of Vienna
Even small changes can have major effects, says Prieto-Curiel: “In Vienna, for instance, reducing the daily share of car trips from 27% to 26% would mean almost 4% fewer car journeys—saving roughly six million trips per year.”
Global railway systems by metro and tram coverage, length, stations, and ridership: The number of cities with a metro and tram system between 1870 and 2020 can be seen on the left. On the right are the global length of the system, the number of stations (or stops), and the number of passengers each year. Based on data from the International Association of Public Transport.
Trams: Historical Development and Current Role
Trams experienced their golden age in the 1930s, when about 900 cities worldwide operated networks. As private car ownership grew, however, many systems were dismantled: by the mid-20th century, nearly two-thirds had disappeared, and by the early 1990s only fewer than 300 cities still had trams.
In recent decades, trams have been making a comeback. By 2020, a little over 400 cities had trams, serving an estimated 14.7 billion passengers annually. Europe is the global stronghold of this mode of transport, accounting for nearly 60% of total network length and around 75% of all passengers.
Metros, by contrast, were operating in just over 190 cities worldwide in 2020—but carried 58.3 billion passengers, roughly four times more than trams.
“Choosing the best means of transport is a central challenge for cities,” Prieto-Curiel says. Metros can move many people quickly across long distances, but are expensive and therefore found in fewer places. Trams are often seen as a more affordable alternative.
“But when it comes to reducing car traffic, the study clearly shows that public transport systems differ greatly in their effectiveness,” he explains. Because trams are typically slower and have lower capacity than metros, they do not reduce car use to the same extent, according to Prieto-Curiel.
Global Relevance: Sustainable Urban Mobility
Cities worldwide are increasingly promoting active mobility and public transport to reduce car dependency and its many negative consequences—such as noise, air pollution, land sealing, traffic congestion, and health burdens.
“The study clearly shows that high-capacity public transport is a key driver of sustainable urban mobility. Even a small reduction in car use can generate significant collective benefits,” says Prieto-Curiel.
While trams are often seen as a cost-effective alternative to metro systems, the study shows that metro networks measurably reduce car traffic, whereas this effect cannot be observed for trams.
About the Study
The study “Metros reduce car use in European cities but trams do not” by R. Prieto-Curiel was published in Nature Cities (doi: 10.1038/s44284-025-00342-7).
About CSH
The Complexity Science Hub (CSH) is Europe’s research center for the study of complex systems. We derive meaning from data from a range of disciplines – economics, medicine, ecology, and the social sciences – as a basis for actionable solutions for a better world. CSH members are Austrian Institute of Technology (AIT), BOKU University, Central European University (CEU), Graz University of Technology, Interdisciplinary Transformation University Austria (IT:U), Medical University of Vienna, TU Wien, University of Continuing Education Krems, Vetmeduni Vienna, Vienna University of Economics and Business, and Austrian Economic Chambers (WKO).
