Global temperatures are rising and weather events are becoming more extreme. Last year (2020) was one of the hottest on record and 2021 is expected to exceed those numbers once again. “In this case, first place is the worst place to be,” commented Rick Spinrad of the US National Oceanic and Atmospheric Administration in early August 2021: “July is typically the world’s warmest month of the year, but July 2021 outdid itself as both the hottest July and the hottest month ever recorded. This new record adds to the disturbing and disruptive path that climate change has set for the globe.”
Severe heatwaves struck North America during June and July, with many places exceeding previous highs by 4-6°C, causing hundreds of additional heat-related deaths. On 9 July, South California’s Death Valley saw the highest temperature ever documented on land, a staggering 54.4°C (130°F).
Sadly, this wasn’t a freak event. On 11 August, a weather station in Sicily reached 48.8°C, a new European record, while Kairouan (Tunisia) reached 50.3°C – yet another milestone high.
At the other end of the thermometer, abnormally cold conditions similarly affected many parts of the world at the start of 2021. Winter Storm Uri caused an estimated USD21bn in damage as it swept across the US in February, knocking out power grids, devastating transport networks, and resulting in over 200 deaths. Texas experienced its lowest temperatures in three decades. On the other side of the Atlantic, an aberrant cold front hit Europe in early April, with average temperatures around a degree lower than seen in decades.
Aside from extremes of hot and cold, stronger than usual rain and wind events were also seen in 2021. Around 720mm of rain fell on China’s Henan Province between 17-21 July, with the city of Zhengzhou deluged by 201.9mm in one hour (a Chinese national record) on 20 July. Around 382mm of rain fell in six hours, with the city seeing three times its annual average in just three days. The resulting flash floods were linked to more than 302 deaths, including 14 on the city’s metro that filled with water. Reported economic losses totalled USD17.7bn.
Western Europe similarly experienced severe flooding events in mid-July. Western Germany and eastern Belgium received 100-160mm of rain on 14-15 July over already saturated ground, causing flooding and landslides and resulting in more than 200 deaths.
Our climate is becoming ever-more unpredictable, and we are at its mercy.
The effect on transport
Within our built environment, primarily formed of glass, steel, asphalt, and concrete, dangerous heat islands are increasing the risks of heat stress and the effects on urban transport networks have been devastating.
As temperatures across the Pacific Northwest soared in the summer of 2021, the US city of Portland suffered three of its hottest ever days on 26-28 June, forcing the closure of both MAX and Streetcar service as power cables melted and equipment overheated and failed as the mercury hit over 40°C – and kept climbing. MAX LRVs, like most light rail systems, are powered via overhead copper wires which expand as temperatures rise. As they expand, they sag and with such sustained high temperatures, the counterweights designed to keep the wires taut hit the ground, therefore the wires to continued to sag.
Transit authority TriMet explained that while MAX is designed to operate in conditions up to 43°C, when the temperatures hit two degrees above this on Sunday 27 June power grids were overwhelmed. As an added obstacle, the heatwave didn’t abate overnight as much as expected, leaving no respite for the system to cool down ahead of the next day when temperatures went up once again, exceeding 47°C.
Previously an issue for environmental specialists, the effects of climate change on our planet’s weather systems are forcing us to rethink the way we design, build and operate infrastructure. This is also no longer an isolated issue as international contexts and climate emergency awareness has shifted the debate from the background into the mainstream.
As Christelle Chichignoud, Sustainability Director at global consulting and engineering specialist SYSTRA, explained at the UK Light Rail Conference in July 2021: “What will the world be like in 2050 when we arrive at this famous deadline of a low carbon world? Good question, but today we plan, design and operate for a broad range of climate conditions based on experience with historic climate. Because of climate change, this historical information is becoming less and less relevant.”
But as these considerations now sit equally alongside economics, security, safety and passenger comfort, land use and ecology, energy and consumption, materials and waste management, thinking around resilience in the equation is also about finding the right balance.
A 2015 study into tramway performance in Melbourne illustrated the effects of extreme weather conditions on its network. On hot days, trams require increased maintenance to address mechanical faults, while on wet days traffic conditions and flash flooding can cause delays or alteration of services.
As more than 80% of Melbourne’s tramway operates in mixed traffic, the interaction between other road users and trams can have dramatic effects. Heavy rain or high temperatures may drive would-be public transport users to their cars, increasing congestion and travel times for all modes. Emphasising this, the report suggests that, for example, every additional millimetre of rain in the morning peak increases journey times by around eight seconds per trip.
Braving the heat
As summers get drier and hotter it is instructive to look at new tramways in more extreme climates.
Also at the 2021 UK Light Rail Conference, SYSTRA’s Hervé Mazzoni presented a number of international case studies of the company’s involvement in adapting new light rail installations to meet both current and future climate conditions.
Beginning in sub-Saharan Africa, Mr Mazzoni explained: “Ouargla is a hot city in the middle of the desert in Algeria where the ambient temperature can reach up to 55°C. Temperatures can be much higher in the equipment cabinets, so while it is important to protect the passengers and the operator it is equally important to protect the equipment and infrastructure.”
To address the extreme conditions in this inhospitable environment, SYSTRA came up with a ‘low carbon architectural design’ that reduced the energy demand in system construction, optimising the orientation, form and envelope of the system’s buildings to address their thermal performance. As far as possible, natural ventilation and free cooling solutions were employed to reduce the need for mechanical air conditioning systems – although they were still essential for the tramway’s workshops and control centre.
Mr Mazzoni continued: “We rediscovered the benefit of what they call the Arabic ‘Mashrabiya’, a half-closed, half open window that lets the air flow and reduces the level of temperature entering the building.”
As well as the operational buildings, all 16 stops on the 9.6km (six-mile) line incorporate Mashrabiya architectural elements to provide added protection from the scorching summer temperatures.
The arid landscape in Ouargla posed another major challenge: sand. This can build up very quickly, acting aggressively on metal components as it also contains high levels of salt. A new design for the switches was created by SYSTRA that lets the sand flow and collect in trays. This clever solution is used in conjunction with equipment that sucks sand away from switch blades similar to a vacuum cleaner.
Ouargla’s tramway, which opened in March 2018, also features rolling stock engineered specifically to withstand the extreme temperatures and intense solar radiation. These adaptations include heavy-duty air-conditioning, solar protection film, a special exterior paint and enclosure of exposed components such as traction and braking systems and the trams’ pantographs. The double-ended 43.9m trams are similarly stabled in enclosed, air-conditioned facilities.
Yet even with such mitigations, when temperatures are particularly high it is necessary to limit the duties of each vehicle to no more than four hours, after which a replacement is provided to allow the first unit to return to the covered depot for cooling-off.
Many of the climate resilience innovations employed in Ouargla had their basis in another SYSTRA-designed tramway project – the Dubai Tram which opened in November 2014. The Middle Eastern Emirate has many similarities (with up to 50°C temperatures and 100% humidity), although different compromises were required on this project to meet the aspirations of the client.
To cope with the extreme heat, all 11 stations are fully-enclosed and feature air-conditioning and platform screen doors. Substations and equipment rooms were built underground to use common cooling systems: “We wanted to limit the volume that should be ideally air-conditioned to save energy – but after our calculations we ended up with a solution to cool the whole volume of the station. We thought we could save energy at that level, but it was not possible because of the high ambient temperature,” Mr Mazzoni explained. “We also buried some of the electrical equipment underneath the stations as one big air conditioning unit has much better efficiency than two small ones.”
Some compromises were made in light of both economics and technological maturity, and not all of the original design ideas were employed in the competed system. Mr Mazzoni commented: “We suggested double glazing for the rolling stock to limit the interior temperature, but this would have such a significant impact on the weight of the vehicle that we didn’t keep this solution.”
Instead, the version of the Alstom Citadis that serves Dubai was modified with uprated air conditioning in the cab and passenger saloons, as well as including UV-resistant paint, glue, decals, cabling and electronics, and UV-protected windows were also used.
With a requirement for ground-level power supply, SYSTRA’s design teams came up with an ingenious ‘low-tech’ way of maintaining a consistent connection in a location where sand could easily create a barrier between the trams’ collection shoes and the supply. This was eventually solved by fitting each tram with heavy duty brushes to keep the contact strips clear.
One extreme to another
Tramways in places where sub-zero temperatures and winter snowfalls are common are well-used to the adoption of precautionary measures to ensure that operation can continue even in the most adverse conditions. Trams run after hours to keep tracks and overhead lines clear of snow and ice build-up, often running throughout the night. However, drifting snow and ice can frustrate these efforts as it only takes relatively small amounts of either to block tracks and switches and interfere with substations and signalling equipment.
Deteriorating conditions thus make it important to install devices such as point heaters to keep equipment going. As well as ice on the overhead lines themselves, heavy snow and ice can accumulate on trees and branches causing them to hang or fall onto the track or OLE. This should not result in wholesale removal of trees as a defensive measure, however, but it does require additional maintenance of trackside vegetation depending on the season.
Similarly, vehicles can suffer from the elements. Ice accumulation on the overhead can cause arcing of current, which damages the pantographs and can even go as far as to cause ‘snags’, which in the worst-case scenario could pull down the overhead wire. To combat this, some systems employ specialist cars with ‘sleet-cutter’ pantographs, although where this is not economic ice-breaking pantographs are added to existing rolling stock.
It is also important to review the passenger environment, so under-platform or waiting area heating can be considered for the harshest climates and measures should be taken to ensure, for example, that doors can open and close reliably in sub-zero temperatures. For this reason, covered and even heated stabling facilities are worthy of investigation in changeable climates; there are few things worse for rail passengers than having to deal with a late or cancelled service because of faulty doors.
Where trams share road space with rubber-tyred vehicles, there can be additional issues with skidding vehicles obstructing the tram’s path. Many local authorities use salt or abrasive chloride or acetate-based treatments to de-ice roads, but their corrosive effects on metals, and even concrete and asphalt, must be taken into consideration. Areas exposed to splashback need to be arranged so that these de-icing treatments cannot easily penetrate into sensitive equipment, reducing their lifespan or reliable operation.
As SYSTRA is the technical design advisor for Québec City’s tramway project, now planned to open in 2028, Mr Mazzoni presented some of the climate-related design proposals for this new 19.3km (12-mile) system: “During the long five months of winter, the city is exposed to severe snowfalls and ice formation. Heating switches is a proven solution in cold countries all around the world, but generally railways use a form of gas heater and you obviously cannot put this in the middle of the street.
“In Québec we proposed a reinforced heating system for the switches, a solution that doesn’t exist off the shelf. Another point is the contact wire. Ice can destroy the pantograph carbon so contact is lost with the overhead line. Heating the contact line is something that is well-known in the railway world, but for a tramway we proposed improved electrical sectioning to keep the catenary warm at night when the temperatures fall.”
Highlighting the close relationship of the tramway with the overall fabric of the city, the importance of interfacing with urban designers is key, Eric Le Hir, Project Director for the Quebec system, added to Mr Mazzoni’s comments: “The city created oversized pavements on both sides of the street, as what do you do when you have two-metre high mountains of snow once you have cleared the tracks?
“People forget that Québec City had a tramway from 1897-1948, but back then people maybe accepted there would be times when it was out of service. That is not an option for today.”
As well as greater extremes of hot and cold, our planet is getting windier, too. An often-overlooked area of climate change, a 2019 study found that average global wind speeds over the previous decade increased by 6% (11km/h to 12km/h – 7mph to 7.4mph). While this is good news for wind turbines, significant rises in wind speeds pose new risks to overhead equipment.
Higher crosswinds can lead to pantographs slipping off the wire and becoming entangled, tearing down equipment and immobilising the tram. Simplifying overhead with single trolleywire, supported by robust spanwires attached to buildings or to trackside columns is one remedy we might suggest for this situation.
Preparing for the future
In the wake of November’s COP26 climate change conference in Glasgow, a number of key truths emerged that will shape the future of our society. Firstly, the key target of halving global emissions over the coming decade is going to be a significant challenge. Secondly, every year that passes without significant reductions will likely see an increase in extreme weather conditions. Previous ‘storm of the century’ events are becoming more common and previous temperature, precipitation and wind speed records could well be broken far more regularly.
The design, operation and maintenance of transportation networks must adapt to take account of this new reality. With this comes the twin challenges of minimising environmental impacts in construction and maintaining frugality in energy consumption, alongside making new infrastructure more resilient – at the same time placing these within the existing framework of ensuring that light rail systems remain attractive, accessible and economically achievable. The performance of a system cannot be compromised, especially in environments with extreme climates, but the comforts that operating staff and passengers are used to must also be maintained. While we can try to find solutions that best meet these ‘big’ issues, the end story is always one of compromise – but a particularly difficult one to gauge given the uncertainties of climate change.
It is obviously easier, and arguably less costly, to create climate-resilient infrastructure at the design stage. However, with all of the issues outlined in this article there will also be a need to consider the changing climate more closely with existing infrastructure in a more detailed way than just observing the normal changing of the seasons.
As Mr Mazzoni explains: “There is probably not a pre-fabricated solution for everything, but if we think of overheating for example, there will likely be a need for extra ventilation of technical rooms.
“Solutions for vehicles are probably more difficult. If you have to retrofit air-conditioning, you probably have to replace or substitute existing equipment with new systems, but these will likely be heavier and the structure of the car body may not be able to support the additional weight. So we need to think about re-engineering some components of the transport system – and we have a lot of work to do in this direction.”
Article appeared originally in TAUT 1009 (January 2022)