Metros reduce car use in European cities but trams do not

TL;DR

This study asks how European cities with metro systems, tram-only networks, or neither influence car usage. By leveraging the ABC mobility framework and a harmonized CitiesMoving dataset, it analyzes compositional modal shares $(A_i,B_i,C_i)$ across 378 European cities, employing Dirichlet regression to relate shares to infrastructure presence and city size, and a Poisson–Multinomial framework to estimate weekly car journeys. The findings show that metro-equipped cities consistently exhibit a lower car-share $C$ and higher active/public transport shares $A$ and $B$ compared with tram-only or no-rail cities, with effects amplified in larger cities. The work highlights that the benefits of rail-based public transport on reducing car use are strongest for metros, while trams alone do not reliably reduce car dependence, underscoring the need for nuanced policy and infrastructure planning that accounts for city size, network coverage, and service quality.

Abstract

Despite the evident drawbacks, car ownership and usage continue to rise globally, leading to increased pollution and urban sprawl. As alternatives, Active Mobility and Public Transport are promoted for their health, economic, and environmental benefits. However, the efficiency of Public Transport varies widely. Metro systems, in particular, offer a high-capacity, long-distance solution, but they are expensive and only found in a limited number of cities. Trams, on the other hand, may serve as a substitute. This study compares the modal share in European cities, analysing the differences between those that have a metro, a tram, or neither. The analysis draws on a comprehensive dataset from CitiesMoving.com, which compiles and harmonises mobility surveys from around the world according to the ABC framework (A for Active mobility, B for Bus and other forms of Public Transport, and C for Cars). Findings reveal that cities with a metro have a significantly lower share of car journeys than those with only a tram or no rail system.

Figures (4)

• Figure 1: Global railway systems by metro and tram coverage, length, stations, and ridership. Left - Number of cities with a metro and a tram system between 1870 and 2020. Right - Global length of the system, number of stations (or stops) and yearly passengers for metro and tram. Data from UITP2021 and UITP2023.
• Figure 2: $ABC$ framework for 378 cities in Europe. Left - Distribution of the modal share depending on whether they have a metro, only a tram, or no rail system. Right - $ABC$ for the 378 cities in Europe MobilityABCPrietoOspina.
• Figure 3: $ABC$ framework depending on whether cities have a metro, only a tram or none. Left - Average $ABC$ share of cities in Europe with a metro, only a tram or none. The number represents the weighted average of each group, where each city is weighted by its population. Right - $ABC$ share when only cities above $\kappa$ size are considered. Bottom - $ABC$ share for cities with metro, only tram or neither, depending on the size of the population obtained with a Dirichlet regression model for compositional data, using maier2014dirichletregciteR. The model displays the impact of whether the city has a metro, only a tram, or neither, as well as the population.
• Figure 4: Differences observed in the modal share across cities. Left - Differences for $ABC$ (vertical axis) between cities with a metro and cities without a metro (including cities with a tram), depending on the values of $\kappa$ considered (horizontal axis). Right - Differences for $ABC$ between cities with only a tram and cities without a metro or a tram.