As the recent unprecedented heatwave comes to an end, at least temporarily, it seems a good time to reflect on how hot, sunny weather might affect travel behaviour.
Unlike wind-driven storms or winter weather which have much more direct and obvious impacts on transport infrastructure, the physical impacts of heatwaves on roads and public transport are more diffuse. Steel rails may buckle, tarmac occasionally melts, and fewer people may be allowed to crowd onto the London Underground carriages, but mostly roads and services are available for normal use (barring planned engineering works, resurfacing and other construction that often is scheduled in the summer). The heat and talk of beaches and barbecues may make the headlines, but travel disruption much less so. Even where heat and drought result in forest fires, they rarely affect major routes.
Yet heat itself can still be an extreme type of weather as much as cold or wind or rain. And people do change their travel behaviour based on the weather, especially extreme weather. Various studies have shown decreases in trips by different modes in adverse weather. And in countries which regularly experience extreme heat, another study recorded decreases in active travel once temperatures pass a certain threshold.
However, it is not regular for the UK or many of the other countries that have been affected by this summer’s heatwaves to experience extremely hot weather. That makes it difficult to hypothesise how people might respond in terms of travel behaviour. Especially as these heatwaves are only extreme in relative terms – temperatures are still not reaching the levels common in tropical or desert countries, so it is not necessarily too hot for people to walk, bicycle, or otherwise want to be outdoors and enjoy the weather when they travel. Alternatively, the lack of familiarity with such weather may result in people struggling to adjust and seeking travel spaces that are air-conditioned, mainly cars, but also, in some areas, a subset of public transport services.
Or it may depend on where people are going or where they live. How comfortable are different houses or apartments in the heat? How about offices or shops? Are private gardens or public parks more readily available? Which are more likely to provide relief from the even hotter microclimates of urban streets? The answers to such questions may suggest less travel altogether, but the possibility of empirical, quantitative evidence to support this is confounded by yet another factor. Holidays.
Days of extreme heat occur in the summer, when there are often fewer regular, short-distance trips and more long-distance travel for leisure purposes. People often plan such trips well in advance and can’t change travel arrangements nimbly. Thus, families with school children, those who work in education, and various other groups are likely to change their travel behaviour in the summer no matter what weather summer brings. There is consistently less traffic during summer school holidays. There is also usually more walking and cycling, more sporting events and festivals. Such activities are often only cancelled for electrical storms or other immediate dangers; unusual heat or drought is not among these dangers.
Still, even if current travel behaviour during heatwaves cannot easily be tracked, that does not mean that we should not use this unusually long heatwave to try to monitor how people have responded. Nor does it mean we should not work to adapt our transport networks to the likelihood of future, more frequent hot weather. We could stress our steel rails to higher temperatures and ensure we use appropriate aggregate mixes to prevent melt, but also we could provide more public water fountains and street trees to help people walking and cycling to re-hydrate and cool off. I have written before that one way forward for resilience is ‘monitor and adapt’, and this summer provides a perfect opportunity to start such a process.