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Hi Nick! Your recent article in Nature explores the impacts of extreme heat in the context of transportation systems, including the significant health risks for commuters and transportation workers. The roap map your team proposes to address these risks calls for a coordinated approach that includes better heat governance, monitoring, adaptation measures, and targeted public health strategies that address heat equity.

Firstly, can you tell us a bit about how this framework came to be? 

We initiated this work in summer 2022 at a time when heatwaves in multiple regions were fuelling public and media concern about extreme heat. But interestingly, the angle that most captured news headlines in my home country (the UK) was the heatwave’s impact on transport. The national rail operator had imposed speed restrictions amid a succession of 40°C days; newspapers reported that the cost could total tens of millions of pounds per day in lost economic output.

Our team was organizing heat resilience workshops around this same time to help city administrations develop extreme heat action plans, and we were struck by how often local participants mentioned the transport sector as an important setting for action.

We worked with Professor Satish Ukkusuri at Purdue University to convene a working group of global experts who could help us understand this urgent and complex set of challenges – including both their engineering and public health dimensions. Sang Ung Park and Shagun Mittal from Prof. Ukkusuri’s lab conducted a comprehensive literature search; we then brought together a panel of academics and transport managers from four continents to debate the facts and put forward recommendations.

What do you view as the main barriers to addressing heat health risks in transportation systems? 

It’s helpful to think of at least three different levels at which extreme heat risks play out in the transport sector.

Firstly, high temperatures affect the physical materials that transport assets are made of: they can cause asphalt to melt, steel to expand, and signaling equipment to malfunction. Engineering knowledge and a better understanding of the business case for heat resilience are among important barriers here.

Secondly, heat waves affect the decisions of transport users (or what transport planners call ‘trip demand’). Demand for public transport trips can follow an inverted U-shaped curve with respect to temperature. On hot days people may postpone trips or opt for private vehicles instead – particularly if facilities aren’t designed with thermal comfort in mind – with unfortunate implications for revenue and system utilization. 

Thirdly, heat affects human health in transport settings. This impact runs in two directions: features of the transport system can magnify ill health; but ill health can also affect performance of transport systems. Passenger health is a notably strong determinant of system performance on busy transit systems. If just one subway passenger pulls the emergency cord when a train is in a tunnel – as happens much more frequently during heatways – major network-wide delays can result. Investing in passenger communications to encourage behaviors like carrying water and not boarding trains if feeling unwell can help transport operators hit performance targets in terms of reduced delays.

On the other side of the equation, transport trips can be the setting for a large number of cumulative hours exposure to dangerously high temperatures. This adds to health burdens of vulnerable populations and has particular effects for women considering strong links between heat exposure and adverse pregnancy and maternal health outcomes. In sum, the case for transport operators addressing heat risks in a comprehensive manner is strong. 

Health-wise, is there available data on who suffers most when heat impacts transportation systems?

There is not much hard data on the health impacts of heat in transport. But transport user surveys paint a picture of which socioeconomic groups spend more time on modes of transport that we know to be hotter. Take urban transport in Mumbai, where 63% of poor households walk to work compared to 44% of commuters as a whole.

Or consider minibus taxis in South Africa, which accounts for some 80% of public transport trips in the country serving 16 million people per day. The South African Medical Research Council, working with our team, conducted measurements within minibus taxis last summer, and found that heat stress can exceed levels categorized as “extreme caution” for as much as 10 hours on a typical summer’s day.

In these and other cases, a focus on “heat equity” is important since poor and marginalized individuals often face more cumulative heat exposure hours as well as being more susceptible to a given heat exposure. We need case-by-case research to understand whether this holds true in other locations, and more importantly, to plan interventions to address it.

What do you see as the role for the public health sector in supporting the efforts outlined in your road map?

Transport stakeholders have the lead role to play on many of the challenges we identify such as engineering road, rail and air transport systems to perform better in heat extremes. It’s also worth stating that there is no single template for the governance of heat risks: health ministries have historically taken the lead in some countries, emergency management departments in others, while subnational administrations like cities have driven the agenda elsewhere.  But whatever the institutional setting, public health expertise is likely to be crucial in making an effective plan to prepare transport systems for more frequent and intense heatwaves in coming decades – extreme heat affects steel and asphalt but also affects human lives.

Do you have any examples of cities or countries that are successfully protecting commuters and transportation workers in the face of rising heat?

Yes, here are three examples that I found instructive. 

In our recent study ‘Unlivable: What the Urban Heat Island Effect Means for East Asia’s Cities’, we highlight Japan’s national program of heat harm reduction which links temperature thresholds that are known to predict ill health with a wide range of sector specific actions. It is an important example of a comprehensive multi-agency effort based on science.

Secondly, we have learned a lot from the Heat Action Plan pioneered by the city of Ahmedabad in India since 2013. It is notable that traffic police, who work long hours in exposed sun, were directly consulted as part of the groundwork for this plan.

Thirdly, we learned from remarkable work at Transport for London on building data collection and indicator frameworks to help drive improved resilience to heatwaves. You can only manage what you measure, and TfL has been addressing measurement issues around heat as part of a comprehensive response to climate risks more broadly. 

Do you have any projects or initiatives to advance the implementation of this road map in the works?

At the Global Facility for Disaster Reduction and Recovery, we have a Global Program for Resilient Infrastructure which provides grant financing and technical expertise to integrate disaster resilience in infrastructure investments around the world. Heat resilience is one of our emerging themes within this and our City Resilience Program. We have several studies on heat in transport underway – such as helping a rail operator in an African city develop thermal comfort guidelines for new train stations – and more activities in the pipeline (watch this space).

We need to prepare our transport systems for heatwaves — here’s how
 

Learn more: Heat in the Environment

Learn more: Heat in the City