The bridges enable measures to improve the urban climate in their extended surroundings

Measures are also being implemented in the vicinity of Frankfurt's bridges to positively influence the city climate: The evaporative coolness in the city centre is promoted by using the bridge ring line to unseal, plant and irrigate 40,000 m2 area in Frankfurt and to supply a further 200,000 m2 of green space next to and near the bridge with water. The bridges' water system will also enable the planting and supply of around 1,000 more trees in the city centre, which will also improve their microclimatic environment by casting shade, binding pollutants and producing fresh air. In addition, road surfaces will be renewed in the course of the bridge construction. Instead of the traditional dark grey, they will now be finished in a lighter colour with regard to summer heat, which will allow the albedo effect to take effect there.

Chapter content: The chapter describes the package of measures that will be implemented in the bridge context to improve the urban climate

The most important bundle of measures deals with the unsealing and planting of areas in the city, as well as the irrigation of already existing, undersupplied green areas.

By pushing autonomous traffic concepts, a large part of the parking spaces in Frankfurt will no longer be needed in the future - and will thus be available for further unsealing and greening measures as well as tree planting.

Many areas next to the Frankfurt bridges are also designed to be as brightly coloured as possible, so that they heat up less in the summer.

In the course of the construction of the Frankfurt bridges, numerous other positive measures for the urban climate can be implemented

Make the roadsides to the right and left of bridges capable of infiltration: If, during heavy rainfall in summer, the precipitation infiltrates instead of being "disposed of" in the sewage system, then not only is the infiltration area itself cooled, but even long after the rain has stopped, the ambient temperature is lowered by extracting heat from the air for the evaporation of the water. In climatology, we therefore also speak of "evaporative cooling" and the "oasis effect" of green spaces. However, in order to make them capable of infiltration, areas must also be changed in the subsoil.

In total, more than 40,000 square metres of new unsealed and planted areas can be created in Frankfurt's city centre - thanks to the bridges' water system

Stiftung Altes Neuland Frankfurt GNU / Google Satellite

Evaporative cooling through infiltrative surfaces - a drop in the ocean?

In the case of land unsealing and its impact on the local urban climate, three types of unsealing must be distinguished:

1. simply unsealed area covering the water-absorbing space with soil, gravel or grating

2. unsealed area covered exclusively with grass

3. unsealed area with denser and higher plant cover

Compared to darkly asphalted surfaces, both simply unsealed surfaces and lawns are a thermal enrichment:

A grassy parking lot surface, for example, has surface temperature differences of up to 8 °C on hot summer days compared to an asphalt surface (if it is not dried out, of course).

However, even better than simply unsealing or providing lawns is to plant the areas with lush vegetation such as shrubs or perennials.

However, large-crowned trees are the most suitable: as large shade trees, they have the highest cooling effect among urban vegetation, because shade causes more significant cooling in the area close to the ground than evaporation in the canopy further away from the ground. However, since it is often possible to unseal but not always to plant a tree, unsealing is another important urban planning measure alongside facade and roof greening to increase evaporative cooling.

Good urban planning ensures unsealing and infiltration - even where nothing can be planted

In order to allow stormwater to infiltrate in a city during heavy rain events, not only must surfaces be made permeable, but spaces must be created in the subsoil where water can collect.

These spaces can either be actual voids with a grate-like cover over them; or they can be filled with coarser gravel to finish on top with a denser, firmer, but water-permeable layer.

In this way, formerly sealed parking lots or street medians can be unsealed and contribute to the creation of the "water-sensitive" city of the future.

In the course of the construction of the Frankfurt bridges, road surfaces will be renewed after completion of construction anyway, so that for the areas to the right and left of the bridges with a certain gradient, drainage or infiltration can also be achieved under the asphalted road space. Frankfurt can thus take another step towards becoming a "sponge city".

The most important contribution of the Frankfurt bridges to the unsealing of the city: Reduction of the number of vehicles and thus of the required parking spaces - through autonomous, centrally controlled urban traffic

With the autonomous traffic on the Frankfurt bridges, the world's largest inner-city quarter is being created in which a complete world of demand is actually covered by self-driving vehicles. This unique and state-of-the-art test area is the starting point for successively implementing autonomous traffic under the bridges in certain parts of the city or zones - as soon as the systems are sophisticated and the learning curves have been run through.

A transfer to city districts or zones under the bridges can only be expected in a few decades and will also have to work with a transition period: During this time, vehicles will still be individually steered and will only become autonomously driven or controlled by a control center as soon as they enter such a district zone. Up to the limits of these zones, they will have to remain individually steerable.

This means that there is still a long way to go - forecasts assume half a century or more.

Freed-up parking space can be converted into green areas or cycle paths

But when this development towards autonomous urban traffic is complete, the number of vehicles required (including "individually transporting vehicles") will be reduced by up to 90 %. Accordingly, the required parking space in Frankfurt will also decrease significantly.

If parking spaces today presumably take up around 9 km2 of the 52 square kilometres of traffic area in Frankfurt, this will then be less than 1 km2 . This means that 8 km2 can be unsealed and greened or even planted with trees. Entire streets will be given a different look - and a different thermal urban climate.

Experts on the Topic

Universität Augsburg - Institut für Geographie - Stadt- und Geländeklimatologie — HU Berlin - Geographisches Institut - Klimageographie — TU Braunschweig - Institut für Geoökologie - Abteilung Klimatologie und Umweltmeteorologie — TU Dresden - Institut für Hydrologie und Meteorologie - AG Stadtklima — Karlsruher Institut für Technologie - Institut für Meteorologie und Klimaforschung - Atmosphärische Umweltforschung (IMK-IFU) - Stadtforschung — Deutsches Institut für Urbanistik Köln

Good urban planning relies on the albedo effect wherever

Create lighter surfaces to the right and left of the bridges: When the sun hits bright surfaces on hot days, they do not heat up as much as dark surfaces: This is because more of the incident solar radiation is reflected and the reflected radiation is not available to heat the human body, for example. In climatology, this effect is called the "albedo effect". It is traditionally used in hot countries, which is why you find so many lighter buildings and paving stones in southern Europe.

If the pavement is renewed in the course of bridge construction in a street, the pavements to the right and left of the construction site can also be renewed. Large city centres in particular benefit from lighter surfaces - thermally, but also visually. But beware: bright surfaces contribute to the well-being of walkers, but they must not be glaringly bright - otherwise they have the opposite effect and reduce the sense of well-being.

The principle of making all new surfaces in the road area light-coloured is of course also followed on the bridges themselves

Traffic and walking paths on the bridges are always brightly designed

Experts on the Topic

Universität Duisburg Essen - Lehrstuhl für Angewandte Klimatologie und Landschaftsökologie — Karlsruher Institut für Technologie - Institut für Meteorologie und Klimaforschung - Atmosphärische Umweltforschung (IMK-IFU) - Stadtforschung

Conclusion: The multifaceted bundle of measures away from Frankfurt's bridges gives the entire city a more pleasant climate

The Frankfurt bridges will not only change the appearance of Frankfurt along the bridge network. More distant areas of the city will also be upgraded with the help of a wide-ranging bundle of measures made possible by the bridges' water system:

Many surfaces in the vicinity of the Frankfurt bridges are being unsealed, greened and planted; this allows more water to evaporate and lower the ambient temperature. At the same time, many surfaces are being made as light as possible to counteract heating of the air on hot summer days. In addition, the numerous newly planted trees provide cooling shade.

In the long term, Frankfurt bridges will reduce the need for highly sealed traffic areas through their autonomous traffic. Parking spaces that have become superfluous can then also be landscaped or planted with trees and have a positive impact on the urban climate.

Verbesserung des Stadtklimas

Frankfurt: Stadtklima aktuell

Auswirkungen der Brücken

Die CO2-Bilanz der Brücken

Stadtklima – Weltklima

Das Ziel: Die Stadt gegen Trockenheit und Flut wappnen

Die grüne Zukunftsmetropole

Vitalisierung des Stadtgrüns