GREEN TRAMWAY TRACKS – A FLAWLESS NATURE-BASED SOLUTION FOR URBAN GREENING?

 

By Jakub Osmański

 

Although they had been known and used for over 100 years, the interest in green tram tracks and their application have been gaining momentum all over the world just recently. What’s all the fuss about it?

Proponents of green tram tracks point out that they serve as precipitation storage, relieving the sewage systems in case of stormwater runoff. They allegedly decrease the reflection of noise coming from the trams and contribute to lowering the effect of urban heat island. Last but not least, they just look better than conventional tram tracks with concrete or rubble foundations – and it is proven that the presence of greenery around us positively affects our health. In other words, the unbeneficial impact of trams on the environment is reduced. So, a silver bullet solution? Let’s take a closer look.  

For the clarity of the analysis, all consulted literature revolved around the temperate climate and Central-European cities.

The three most common solutions for greening the tracks emerge from the research on the temperate climate. These are: grass; low-maintained grass with ruderal plants; and sedum, a succulent, which looks like that:

We need to bear in mind that tram tracks could create precarious conditions for plants due to limited shade and heavy irradiation. Thus, slowly growing species of short height and low nutrient demands are favored. “Weeds” and sedum do not need to be mowed or irrigated. Thus, they grab an easy victory, since their maintenance needs are very limited compared to the grass which requires it quite often. More effort here might mean less sustainability.

The urban heat island effect is a serious phenomenon, resulting in higher temperatures inside the city center, where the built environment is denser, and basically where concrete (which heats up easily) has the upper hand over greenery. With climatic anomalies becoming more frequent, its minimalization is desired as never before.

Consequent building up of more space with concrete at the expense of greenery makes it even more difficult to hamper the floods – that is where the hydrophilic species step up to absorb rainwater. Studies demonstrate that sedum and grass are capable of retaining, respectively, 50% and 70% of the annual precipitation onto their areas, whereas during the summer grass can hold up to 90%! This is explicable by the metabolism of grass that opens its stomata to exchange gas during the daytime. This allows for receiving more water. Sedum, on the other hand, opens its stomata at night, that in turn lets it endure in much higher temperatures.

Telling calculations from Berlin show that its whole 45 km network of grass tracks after a rainy day can contribute to cooling down 5 km³ of air by 10 degrees. Although grass excels in water storage, there are virtually no differences when it comes to the ability to reflect sunlight, and the succulents alone are believed to reduce temperatures by the tracks by 5-7 degrees.

Sedum does not retain as many harmful fine particles or CO₂ as grass or “weeds”, but on the other hand, more pollutants are emitted during grass maintenance processes. The advantages and disadvantages sort of even out this time.

Although often cited as a great benefit, noise cancellation is not that evident due to the implementation of green tracks – various studies say about 1-4 dB gained. The surface of compared plants is too similar to yield different results here. Nevertheless, the valid point of subjective sensations could be raised – regardless of a near-placebo effect, people still perceive green tracks as less disturbing.

Several studies indicated that less- or unmanaged green tracks are more biodiverse than perfectly cared-for lawns. Just like with water retention, less manicured greenery allows the natural processes to happen – after some years the less tolerant wild species would be gone, letting the more suitable, indigenous species, accommodate – tramway habitats could be perfect refuges for endangered and rare species.  And ever since sedum is proven to contribute less to biodiversity than ruderal species, due to competing with and forcing them out, it is still preferable to trimmed grass. Some research demonstrates, though, tram track areas are not very crucial size-wise in contributing to urban biodiversity.

Although studies mainly show vast public support for greening tram tracks, the preferred solution used to be high-maintenance lawns, which is contrary to the biodiversity and sustainability argument. However, with the increasing general consciousness about biological issues in society, this trend tends to reverse, and ruderal, wilder flora is becoming more valued. We can attribute changing perception of green tracks over time, as turf starts to mature. As already said, in the “weeded” surfaces, changes occur, not leaving the observers with the thought of “a forgotten greenery”, whilst keeping the costs to a minimum. The viable option could be opting for a ruderal finish in less generally visible areas while keeping the “prettier” greenery in closer sight of the people.

The choice between grass and sedum may come down to aesthetics, price, and maintenance. I will let the readers decide on the beauty question, but also kindly remind that there is no ultimate solution and no one requires to resort to one species on the entire network! In the temperate climate it is undoubtedly cheaper to use grass, but adding the costs of extensive upkeeping, it becomes less straightforward. Obviously, the conventional tracks are notably the cheapest option – but will that matter then once heatwave or rainstorm come?

PS Let me present a symptomatic case study of different approaches to greening the tram tracks in two Polish cities – Gdańsk and Poznań. Gdańsk is very reluctant to implementation of this nature-based solution, whereas Poznań had already two times more green tracks in 2018 and is confidently developing it further, basically citing the main takeaways from this blog entry. Gdańsk, however, turns its nose at green tracks due to difficulties in the lawns’ maintenance which reflects in bigger costs. The Roads and Greenery Authority spokesperson openly says that the drawbacks are outnumbering the benefits. Is it “concrete-washing” already?

 

CONSULTED WORKS:

BEMBNISTA, B. (2018, December 2). ZDMiKP nie chce w Bydgoszczy zielonych torowisk. Jak na argumenty o kosztach odpowiada Poznań?, Metropolia Bydgoska  https://metropoliabydgoska.pl/zdmikp-nie-chce-w-bydgoszczy-zielonych-torowisk-jak-na-argumenty-o-kosztach-odpowiada-poznan/

JAKUBCOVÁ, E.; HORVÁTHOVÁ, E. Costs and benefits of green tramway tracks. Scientia Agriculturae Bohemica, 2020, 51.4: 99-106.

KALKOWSKI, K. (2020, July 17th). Zielone torowiska—Dlaczego Gdańsk ma ich tak mało?, Puls Gdańska https://pulsgdanska.pl/artykul/zielone-torowiska--dlaczego/1021316

KAPPIS, C., SCHREITER, K. Effect and function of green tram tracks. Grüngleisnetzwerk internet publication, n.d. http://www.gruengleisnetzwerk.de/images/downloads/effects.pdf

RENDEKOVÁ, A., et al. Comparison of the differences in the composition of ruderal flora between conventional tram tracks and managed green tram tracks in the urban ecosystem of the city of Bratislava. Hacquetia, 2022, 21.1: 73-88.

RMTransit (2022, May 17). How to Spruce Up Your Tracks: The Magic of Green Track. https://www.youtube.com/watch?v=UC-aGO-wa5k

SIKORSKI P., et al. Low-maintenance green tram tracks as a socially acceptable solution to greening a city. Urban Forestry & Urban Greening, 2018, 35: 148-164.

STECKLER, P., et al. Green Track–Environmental Performance Evaluation for “Green” Tramway Superstructure. Road and Rail Infrastructure II, 2012, 683-691.

USED PHOTOS

1. Green grass tram track in Gdańsk, Poland; Grzegorz Mehring, gdansk.pl

2. Sedum spurium; cebule.pl

3. Green ruderal tram track in Bratislava, Slovakia; retrieved from: https://greenfond.eu/en/gallery/extensive-green-roof/green-tram-tracks-bratislava-slovakia/

4. Green sedum tram track in Poznań, Poland; Poznańskie Inwestycje Miejskie, retrieved from: https://raportkolejowy.pl/tomasz-plociniczak-poznanskie-inwestycje-miejskie-rozchodnik-rozwiazanie-na-ekstremalne-warunki-zdjecia/