Sustainable Urban Transport: Are cars compatible with cleaner, greener cities?

Graphic depiction of a future city, showing lots of greenery and no cars - instead, walkers, cyclists and trams
Dreams of a low-carbon future (c) James McKay

Lisa Winkler, who worked with Dr Drew Pearce, Professor Jenny Nelson and Dr Oytun Babacan at the Grantham Institute to publish a paper on urban transport policy in Nature Communications, blogs about the role of cars in cities, what is needed for cities to align with a 1.5°C to 2°C world, and the methods and barriers to reducing cars in cities.

Cities are key areas for climate action. Globally, they’re responsible for 70% of carbon emissions and consume two-thirds of the world’s energy. They present a big challenge to decarbonise, with millions of people relying on carbon-intensive services every day. Yet in the case of transport, there is an opportunity to make significant change. Many cities have existing public transport networks which can be improved upon, and within a city, short distances can often be travelled on foot or by bicycle. However, transportation still accounts for 30% of global energy consumption: the largest 20 urban areas in the UK are responsible for nearly half of the UK’s land transport emissions.

To limit climate change to acceptable levels, as set out in the Paris Agreement, the world has a global carbon budget – the remaining carbon emissions that can be released to have a “reasonable” chance of remaining within a 1.5°C or 2°C global average temperature rise. Identifying the fair share of the global carbon budget for particular regions or cities is complicated and highly dependent on the methodology used. Nevertheless the Tyndall Centre provide a meaningful estimate of the regional budget for London based on equity principles in the Paris Agreement.

In our study, we used the Tyndall Budget to explore how transport in London needs to transform in order to meet its carbon budget. We found that car usage needs to be reduced by 72% by 2025, along with accelerating the uptake of energy efficiency technologies. This means that, in just two years, only 1 in 12 trips would be made by car.

Does this sound feasible?

Cities are very complex systems and the reliance on cars is driven by many factors, including urban form (such as the distance to city centres and sub-centres, the connectivity of streets and the accessibility of amenities), existing infrastructure (such as the availability of public transport and safe cycle routes), and the lifestyles of residents. People often rely on cars to access basic services and do not have a feasible and reasonable alternative. For many trips, using a car is the only option, e.g. accessing car-centric shopping complexes and industrial parks, or transporting goods between homes, shops and to recycling centres and skips.

Yet, in comparison to public transport, cars require massive amounts of energy and materials, and take up lots of space. They release more emissions, create air and tyre particle pollution, and are, quite simply, not a scalable solution for the entire human population. They represent the dichotomy of a convenient, comfortable and often idolised individual solution, but on the large scale represent polluted cities with lower levels of wellbeing.

The scale of change needed is huge…

In our study, we explored different changes to urban transport in London, and whether they would enable London to meet its carbon budget. Notably, we found that current policies, including replacing electric and diesel cars with electric cars, would lead to seven times the amount of emissions allowed by the Tyndall carbon budget. Electrification is also too slow – despite the introduction of scrappage schemes. Only 1 in 50 new cars globally are electric, so it would take decades for the entire car fleet to transition away from fossil fuels – decades that we don’t have. Plus, electrifying the UK’s entire car fleet would require an energy supply comparable to the UK’s entire renewable electricity capacity.

Applying modal shifts to how people travel results in the most substantial reduction in emissions due to less car travel activity overall. Although the emissions released from alternative modes, like trains and buses, are increased, active travel and shared transport infrastructure use significantly less resources than private vehicles. They also lead to health benefits from physical activity, whilst creating safer, less polluted streets and freeing up more space in cities. 

Driving less is an example of a demand-side solution, which reduces emissions immediately without needing to wait for new technologies to be developed and deployed. Central to this is the concept of “energy sufficiency”, namely policies that aim to allow a level of energy use to sufficiently meet human needs. Sufficiency policies set a minimum level of activity necessary for wellbeing and a maximum level of activity constrained by planetary boundaries. In this analysis, the upper limit of car travel activity allowed is set by the carbon budget, and a future research avenue includes analysing the minimum travel activity in different modes necessary for wellbeing in cities.

How do we achieve a rapid and massive reduction in car use?

Cutting car use will undoubtedly need a combination of solutions, including lightweight and efficient personal mobility solutions, such as bikes and electric micro mobility, shared fleets, efficient shared and public transport networks, and car-free areas, as well as transformations in urban form in order for services to be easily accessed without cars. 

The 15-minute city, for example, is a strategy to ensure all basic services can be accessed in 15 minutes by walking, cycling or public transport within a city and is being implemented in numerous cities, including Paris. The 15-minutes city is achieved by ensuring developments are mixed-use, creating well-connected and accessible sub-centres in cities and allowing more flexibility in building use and function, so that businesses can operate in residential areas. Central to this sustainable transformation is the concept of a just transition, meaning that changes in the urban fabric and infrastructure should be benefitted by all city residents, and not push lower-income groups away.

This image explores possible futures for African cities, and depicting an inclusive urban future centred on meeting the needs of all income groups. Created by Karl Schulschenk and Blake Robinson for the Post Fossil Cities Contest in 2017

A few more examples of policies designed to reduce the number of cars are given below:

  • For trips that are difficult to complete without a car, such as the transportation of goods, car clubs and shared vehicle fleets would allow access to a vehicle without owning one, and has been shown to reduce the number of car trips.
  • Car-free zones and car-free days can free up urban space to be transformed to green areas, markets and playgrounds, which can lead to beneficial health effects and are likely to lead to higher levels of active mobility.
  • Dynamic road user charging” is a road pricing scheme that considers geographical location as well as the local impacts of using the road on congestion, air pollution, and noise. In such a scheme, urban areas with access to many alternative modes of travel would see higher prices of using roads compared to rural areas, which in turn ensures low-income households pushed to car-dependent areas are not negatively impacted. Previous natural experiments and studies have found road pricing schemes to reduce number of car trips.
  • An immediate halt in urban road building projects, with existing roads repurposed to prioritise active transport, such as the Barcelona ‘Superblock’ model. In London, this would include a halt to projects such as the Silvertown tunnel, which is being built to facilitate more river crossings in cars, and a redirection of funds to develop river crossings for walkers and cyclists.
  • Better planning regulation to ensure new houses and communities can only be built with good transport links and within easy reach of services including shops, health centres and schools.
  • Along with policies that discourage car use, significant improvements should be made in the accessibility, affordability, and connectivity of public transportation.

Why introducing these policies is so difficult

UK climate assembly members voted in favour of most of the above interventions. However, only 17% of UK climate assembly members voted for the scenario which reduces car travel activity most. Concerns around quality of life, especially for disabled communities, restricted choice, feasibility and cost were raised. Thus, reducing car use presents a significant social and behavioural challenge. Whilst extreme and disruptive policies are necessary to avoid worsening effects of climate change globally, current policy framing based on popular vote is not well suited to delivering drastic change in short timescales. Measures to ensure the public is brought on board with the changes required are vital, but currently missing. Running public awareness campaigns about climate change and local-level action, and including the public in local decisions which impact transport infrastructure, is essential. There also needs to be platforms where voices can be heard and these issues can be discussed openly.

In addition, like the Tyndall carbon budget for London, cities need a regional carbon budget in order to establish accountability for their policy packages and to create meaningful and fair targets. Without consensus on such a regional carbon budget, local policymakers do not have a quantifiable target to comply with the Paris Agreement and have no agreement on the level of urgency required for climate policies.

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