Net Zero and Agent-Based Modelling
A systems-based approach that is fundamentally about people.
We are using an agent based model in our work with Transport Infrastructure Ireland to inform their future-looking strategy for Ireland’s road network. One important pillar in this work is the impact of potential options on emissions. Because an agent based approach allows for granular analysis across multiple systems, we can test potential network scenarios and assess their consequences on emissions alongside equity, operational needs, and revenue models.
Reducing carbon emissions from transport and supporting net zero targets requires a systems-based approach. Agent based modelling allows us to explore the interactions of these systems, like electric vehicle (EV) uptake, behaviour change, land use, and infrastructure changes. With an agent based modelling approach, we can also interrogate who is impacted because we can compare the before-and-after impacts on individuals (agents!). We think it’s important to keep people in the centre of city planning.
Net Zero targets
At Arup, and in the City Modelling Lab, our work is motivated by our belief that well designed systems in the built environment can address fundamental challenges. The climate crisis is a global challenge that our colleagues at Arup have been focused on for many years. In the Lab, we think agent based modelling has a role to play in meeting this challenge as well.
We know that net zero within the next 30 years is an achievable, yet ambitious target for most towns, cities and countries. Currently, only 9 countries have committed to net zero targets. However those countries represent an estimated 49% of global GDP. To achieve net-zero, we need to both eliminate carbon emissions, and remove carbon from the atmosphere. As our work supports decision making at the planning-stages of infrastructure and urban design, we believe agent based modelling could be an important tool to propel the strategies and tactics used to limit carbon emissions and achieve net zero.
Role of transport in carbon emissions
Our transportation is currently a major contributor to carbon emissions. In the UK, transport is estimated to account for 20% of the national greenhouse gas emissions (source: Science, 2014). In the US, the transport sector is the largest source of emissions at 28%.
Within transport, “light-duty” vehicles, which include personal vehicles, account for more than half of emissions (source: EPA, 2020). We have evidence that the trend towards private vehicle ownership is growing: we had 750 million vehicles on the road in 2010, globally. By 2050 it is estimated that will grow to 1.5 billion vehicles (source: International Development Economic Council, 2013).
We have yet to see the medium and long-term impacts of COVID-19 on transport behaviours, but road traffic has already returned to pre-pandemic levels in many cities while public transit ridership remains a fraction of ridership in 2019.
Won’t electric vehicles save us?
No. Electric vehicles (EVs) will not save us. Certainly EVs are part of the solution, but an over reliance on EVs to achieve net zero limits the pace of emissions reductions and could inflict unintended consequences that exacerbate other ills of urban living.
The step change needed to reduce emissions from vehicles would require swapping all (or the majority) of private vehicles for electric vehicles. There are technical challenges to achieving this on multiple fronts. EVs remain sources for emissions as long as the electricity source powering their batteries is from coal or gas.
Simply building and delivering enough EVs on the timescales required would be a challenge for the supply chain. Satisfying the increase in electricity required by the EVs is a significant challenge for energy infrastructure, which is often stressed under current demands (source: Phys.Org, 2020).
Let’s assume we solve all these technical challenges, a reliance on EVs to save the day still leaves us vulnerable to “every inch of land…capped with asphalt.” Simply swapping out vehicle demand with EV demand does nothing to change the congestion cities currently face. Cars take up a lot of space in our communities. During the pandemic, we have seen examples of what our cities could look like if we reclaimed space from cars.
Should we build more public transit service?
A car-centric future is problematic, so what about investing in more public transportation? Public transit is definitely part of the solution. However — simply adding more buses to our roads is not guaranteed to reduce emissions.
When a bus is at capacity, it is a very efficient vehicle. When a bus is empty, it is one of the least efficient modes of transport. With systems that are so sensitive to the humans that use them, it is clear we need to have confidence in our interventions and make sure that we understand the context and drivers of human behaviour there.
How do we achieve net zero?
To reduce emissions from transport, we need a plan for tackling the different causes of transport emissions. To achieve net zero we need a plan for:
- shifting the modes people use (behaviour change and low or no-emission transport options),
- making it easier for people to access services via sustainable transport modes (land use),
- ensuring transport infrastructure upgrades make use of technologies that are responsible for low/no carbon emissions (infrastructure change).
Behaviour change.
In the US, 10 billion miles are driven each year, for trips that are shorter than 1 mile. The EPA estimates that eliminating even 50% of these sub-1 mile trips would eliminate 2 million metric tons of carbon emissions per year.
We need to make it easier to travel by foot, bike, and even public transport for trips like these. This might mean making spaces for pedestrians, making pathways safe for vulnerable road users, or supporting more types of mode (e.g. scooters or cargo-bikes.)
We also know that people are making different kinds of trips than they did 10 years ago. We are travelling more to reach leisure facilities or sport facilities than we are for our jobs (source: UK DfT. 2019). As we live with and emerge from COVID-19 restrictions, we expect travel behaviour to look different than pre-COVID-19 life.
Land use
For trips that are longer than 1 mile currently, do they have to be? What if people did not need to travel as far to reach an affordable grocery store, park, school, or place of employment? The concept of a 15 minute city (or even a 1 minute city!) has been embraced by many urban designers — especially as work and life patterns were dramatically altered by COVID-19.
There is a fundamental requirement to achieving this concept: people need all the services they rely on, and preferably, situated close to their residences. There may always be some services that require residents of even the most well balanced 15 minute neighbourhood to leave their neighbourhood. Hospitals, sports stadiums, universities, and friends are just some examples. People need low and no-emissions transport options for these types of trips.
Infrastructure
Our cities will continue to change and planners will make decisions about what infrastructure to replace or build. Carbon emissions are embedded in the very infrastructure of our cities.
We can use low-carbon materials and technologies to build and operate new infrastructure, but we also need to examine the cost of infrastructure decisions in context. For example, how many vehicle trips might a rail line displace? What if the future of work reduces the overall number of people who might use the rail line, compared to the estimated demand pre-COVID-19?
Why is agent based modelling relevant?
With agent based modelling, we can model a range of speculative future scenarios and compare the overall impact on emissions. This approach is driven by evidence about people’s behaviour. What would the impact on emissions be if knowledge-sector employees worked from home 10% of the time? What if they worked from home 40% of the time?
These changes in behaviour have knock-on consequences for public transit farebox revenue and demand for amenities in new locations. Who will be the winners and losers of these changes? How might we support equitable, safe and low-emissions access to opportunities for people who cannot work remotely because they are our essential workers in the service industry, logistics, or gig-economy?
What if a new research campus included a sports stadium for the community and a new grocery store — would these new amenities reduce the number of miles travelled by a community? Could these trips now be completed by foot, or public transport?
It will take a systems-based approach to achieve net zero. Wouldn’t it be helpful if we had a systems-based tool to help us with this complexity?
Find out more
If you are interested in exploring or applying this systems-based approach to your emissions reduction strategy, we want to hear from you: citymodelling@arup.com
You may also be interested in reading more in our sister blog Arup Digital News.
