The researchers called for a collective shift in behaviour to reduce the number of private vehicles in cities. Planning for car-free cities must include a focus on reducing car dependence, promoting fewer and shorter trips, and encouraging walking and cycling as primary modes of local transport and public transport for longer journeys. Cars should only be used for emergencies or special occasions, the researchers said.

On a global scale, cars are being produced faster than the population is growing; 80 million cars were produced, while the population increased by 78 million in 2019. Global car production (including electric cars) contributes 4 per cent of total carbon emissions.

For this study, the researchers created a mathematical model of car use in a city in which residents either used a car on a daily basis or used public transport. As their ‘cost’, they used the length of time journeys take, as this is the biggest factor when deciding how to travel. The baseline for the model was driving with no traffic.

The model can be applied to any city. It is particularly useful when applied to cities in which more than 90 per cent of journeys are by car, such as in Dallas, Houston, and Detroit in the US.

“The city of the future, with millions of people, cannot be constructed around cars and their expensive infrastructure,” said Dr Rafael Prieto Curiel. “In a few decades, we will have cities with 40 or 50 million inhabitants, and these could resemble car parks with 40 or 50 million cars. The idea that we need cars comes from a very pollutant industry and very expensive marketing.”

Modelling one extreme scenario, the researchers used a city of 50 million residents, each with a car of their own. If all residents use a car on a daily basis to try to minimise their commute time, the city reaches extreme levels of congestion, requiring more infrastructure like avenues, car parks, and bridges to accommodate the cars: a worst-case scenario. Under these circumstances, the cost that everyone contributes by driving maximises commuting times.

While it’s generally assumed that improving public transport infrastructure would improve baseline costs, as more residents opt for this over driving, the model showed that even without improving infrastructure, baseline costs could be lowered by reducing the number of people allowed to drive at a time. For example, if one group of people is allowed to drive one week and must use other modes of transport the next, the average commuting time could be reduced by up to 25 per cent with a ‘non-selfish modal share’ where the number of cars on the road is reduced. This would lead to less congestion and, on average, a faster-moving city.

Driving can be discouraged by making clear the local costs of car use – such as congestion and air pollution – as well as through more direct interventions like congestion charges, tolls, and driving and parking controls. Most importantly, cities should make other forms of transport more appealing, such as ensuring that public transport is fast, reliable, secure, and comfortable. London, which has good public transport infrastructure, has additionally implemented congestion charges and low-emission zones. Meanwhile, Mexico City banned some vehicles based on their licence plate, but found that this led to drivers buying older, more polluting vehicles to bypass the restrictions.

Co-author of the study Dr Humberto González Ramírez, of the Université Gustave Eiffel, said: “Currently, much of the land in cities is dedicated to cars. If our goal is to have more liveable and sustainable cities, then we must take part of this land and allocate it to alternative modes of transportation: walking, cycling and public transport.”

The researchers called for a collective shift in behaviour to reduce the number of private vehicles in cities. Planning for car-free cities must include a focus on reducing car dependence, promoting fewer and shorter trips, and encouraging walking and cycling as primary modes of local transport and public transport for longer journeys. Cars should only be used for emergencies or special occasions, the researchers said.

On a global scale, cars are being produced faster than the population is growing; 80 million cars were produced, while the population increased by 78 million in 2019. Global car production (including electric cars) contributes 4 per cent of total carbon emissions.

For this study, the researchers created a mathematical model of car use in a city in which residents either used a car on a daily basis or used public transport. As their ‘cost’, they used the length of time journeys take, as this is the biggest factor when deciding how to travel. The baseline for the model was driving with no traffic.

The model can be applied to any city. It is particularly useful when applied to cities in which more than 90 per cent of journeys are by car, such as in Dallas, Houston, and Detroit in the US.

“The city of the future, with millions of people, cannot be constructed around cars and their expensive infrastructure,” said Dr Rafael Prieto Curiel. “In a few decades, we will have cities with 40 or 50 million inhabitants, and these could resemble car parks with 40 or 50 million cars. The idea that we need cars comes from a very pollutant industry and very expensive marketing.”

Modelling one extreme scenario, the researchers used a city of 50 million residents, each with a car of their own. If all residents use a car on a daily basis to try to minimise their commute time, the city reaches extreme levels of congestion, requiring more infrastructure like avenues, car parks, and bridges to accommodate the cars: a worst-case scenario. Under these circumstances, the cost that everyone contributes by driving maximises commuting times.

While it’s generally assumed that improving public transport infrastructure would improve baseline costs, as more residents opt for this over driving, the model showed that even without improving infrastructure, baseline costs could be lowered by reducing the number of people allowed to drive at a time. For example, if one group of people is allowed to drive one week and must use other modes of transport the next, the average commuting time could be reduced by up to 25 per cent with a ‘non-selfish modal share’ where the number of cars on the road is reduced. This would lead to less congestion and, on average, a faster-moving city.

Driving can be discouraged by making clear the local costs of car use – such as congestion and air pollution – as well as through more direct interventions like congestion charges, tolls, and driving and parking controls. Most importantly, cities should make other forms of transport more appealing, such as ensuring that public transport is fast, reliable, secure, and comfortable. London, which has good public transport infrastructure, has additionally implemented congestion charges and low-emission zones. Meanwhile, Mexico City banned some vehicles based on their licence plate, but found that this led to drivers buying older, more polluting vehicles to bypass the restrictions.

Co-author of the study Dr Humberto González Ramírez, of the Université Gustave Eiffel, said: “Currently, much of the land in cities is dedicated to cars. If our goal is to have more liveable and sustainable cities, then we must take part of this land and allocate it to alternative modes of transportation: walking, cycling and public transport.”