How do we deliver effective transport decarbonization?

Analyze, assess, decide

A new methodology is needed. Here at Arup, we have been working on the basis that analysis and assessment of the carbon reduction impact of different transportation interventions are needed if decision-makers are to be able to effectively prioritize their approach based on robust evidence, especially if some of those decisions seem politically and societally unpalatable in the short or mid-term.

We need to be able to accurately identify and forecast future trends across trip types and purposes and quantify their impact on carbon emissions. This information is vital if we’re to address some looming dilemmas. For example – the whole-life carbon emissions rating of a section of new highway infrastructure could be compared to the carbon impact of delivering new active travel infrastructure that prioritizes walking, cycling, and wheeling across the same region or area. This robust and mutually agreed-upon evidence base would give us all the information (e.g., mode split, distance traveled, emission factors, EV uptake, etc.) needed to develop comprehensive strategies for decarbonizing the transportation sector across various spatial scales.

When decisions are likely to impact user experiences and end in hotly contested debate, this data is absolutely vital. It will be fuel for debate around the challenges and opportunities presented by more sustainable transportation investments, including economic, technical, political, safety, and behavioral considerations. This data is needed if we’re to be able to prioritize investments that have the greatest potential to reduce carbon emissions. It’s data that enables a carbon emissions "business case" to be developed.

Decarbonization: what counts as evidence of success?

Unfortunately for us all, such information at the moment is disparate, incomplete, and full of gaps. While attempts have been made by numerous bodies within the sector, there is no single complete dataset or recognized evidence base that enables these decisions to be made. The latest guidance for local transportation plans in the UK will more than likely emphasize the need to demonstrate "Quantified Carbon Reduction Targets" within municipal transportation plans and to include a strategy to achieve these goals.

As such, we have developed our own in-house Transportation Carbon Assessment Tool (TCAT) to respond to these challenges. This tool pulls together a number of open-source data sources in order to quickly and effectively test the implications of different mode share scenarios on carbon emissions related to transportation. This enables us to rapidly test different interventions and scenarios, working with high-level emissions datasets from the UK’s Department for Energy Security and Net Zero (DESNZ) and develop future modal split assumptions and forecasts, using specialized technical transportation planning and modeling skills.

Creating the tools to support positive change…

We have recently developed this model further to offer our clients custom data-based tools and models that can deliver quantifiable reductions in their GHG emissions from projects or infrastructure they can influence across different sectors. Our work with the Ebbsfleet Development Corporation, where we produced a carbon model that integrated transportation, buildings, and waste elements so they could structure their decarbonization plan in such a way that they could seek to set and deliver ambitious targets that will make tangible changes in their ambition to become net-zero by the completion of their planned Garden City.

At a different scale, we have also recently developed a regional-scale transportation simulation model for Transport East, a partnership body that coordinates policy and strategy for Norfolk, Suffolk, Essex, Southend-on-Sea, and Thurrock. This simulation represents household and freight trips across all modes for the whole region. We tested a variety of scenarios (such as boosting active modes, road charging, and increasing electric vehicle uptake) to measure their emissions reduction potential and develop a robust transportation decarbonization strategy by 2040.

This has predominantly been developed in response to the Transport East strategy and the challenges of transportation decarbonization at a local scale, especially in areas that are polycentric in their built form and have very varied regional characteristics. These often have multiple urban centers and large swaths of rural areas, with underdeveloped sustainable and public transportation networks. This approach allowed us, in collaboration with the client, to test a number of different hypothetical intervention scenarios, such as free bus use for everyone and delivering Dutch-style cycling infrastructure (where cycling is comprehensively catered to and encouraged within the road network).

There are no silver bullets for the decarbonization challenge, of course. Our first-stage modeling established that EV charging and uptake do have an impact on decarbonization and GHG reduction, but it’s not yet a practical energy source for freight vehicles – which remain a major source of road-based emissions. Second, the decarbonization benefits of EVs mostly flow to wealthier groups in society, and the switch to EVs may have undesirable socioeconomic impacts, such as increasing private car use for short trips. Mapping these interlocking effects is key for policymakers keen to craft effective decarbonization solutions. Our work already points to the need for an integrated, multi-modal approach to achieving net-zero transportation – modeling and research work that we continue to pursue.

Progress on all fronts

Like every other climate challenge, transportation decarbonization clearly needs to be tackled from many concurrent angles, with a clear-eyed awareness that the solution will be a blend of technology, regulation, market factors, and behavioral change. With segments of the population finally becoming more environmentally conscious, consumer interest in EVs building, and the topic becoming more mainstream, we need robust tools and analysis of the carbon reduction impact of different transportation interventions to help develop effective and integrated transportation decarbonization strategies that are supported by stakeholders and local communities.