Turf track

In the case of a grass track , sometimes also called green track , the track body is bordered with grass or other vegetation and the space between the rails is greened. It is a popular means to the roadbed of road and rail vehicles visually upgrade. In addition to the positive visual effect, the grass track also has an acoustic effect. The noise emitted by the vehicles is significantly reduced. The rail, set in humus, has no airborne sound radiation and a strongly damped structure-borne sound radiation . The vegetation also absorbs the airborne noise emanating from the rail surface.

There are various types of grass tracks:

Elevated grass track: Grooved rails are laid on normal concrete sleepers and filled with earth up to the top of the rails. This design offers the best sound insulation and the best visual result, as only the running surface and the groove of the rails can be seen. Special chamber filling stones are usually built in to the side of the rails so that the soil does not come into direct contact with the rails. The fastening elements under the profile blocks remain clean and protected against corrosion. If such filler stones are not used, the rails and fasteners corrode more quickly. In addition, the soil must be removed when changing rails. Because of the corrosion caused by the moisture inevitably stored in the ground, the rail fasteners usually also have to be replaced. In addition, these are not accessible during operation and their condition can therefore only be monitored with difficulty. In exceptional cases, high-lying grass tracks can be driven on and crossed with road vehicles.

Low-lying lawn track: A sleeper track is laid on concrete longitudinal beams. Now the spaces between the sleepers are not filled with gravel as usual, but with humus. The rails remain completely free, which reduces the visual effect a little. The sound attenuation is also somewhat lower in this design. On the other hand, it is easier to check and replace the rails, and the fasteners corrode much more slowly because they are not in the ground and are therefore not permanently exposed to moisture. The installation of track switching means is possible, the drifting reverse current into the ground is better prevented, which is advantageous with direct current supply. The use of track circuits is also possible. Finally, in this design, instead of grooved i. A. cheaper and easier to maintain vignole rails are used. In the Alicante Tram but also high-lying turf tracks were laid with Vignoles rails.

The lawn covering requires a permanently secure superstructure, usually in the form of a solid roadway . Ballast superstructure would not be positionally secure due to the entry of soil material and the resulting reduced friction between the ballast stones and the sleepers, nor could it be tamped or straightened due to the lawn covering. Subsequent changes and extensions that are not taken into account and prepared from the outset are significantly more complex than with classic, uncovered ballast superstructure.

Lawn track is planted either with lawn or with easy-care ground cover . Lawn has to be maintained and watered relatively laboriously. Ground cover wilts in times of drought, but requires minimal irrigation. Instead of filling the space between the rails exclusively with soil, lawn paving stones can also be laid.

Connection to the ground

In Würzburg , the Alliance Mobility and Regional Development of Agenda 21 Würzburg sees the cause of the poor drought tolerance of the lawn on the lawn tracks that have been laid out since 2000, for example. B. in the outer Zellerau that they have no connection to the ground, but only consist of a layer of earth on a concrete layer. The condition in these turf tracks is compared with the older tracks, e.g. B. on Mergentheimer Straße (built 1985), where the green was less damaged under the same climatic conditions. A similar phenomenon was also examined by the TU Dresden in a long-term study. However, the connection to the ground requires a solid track .

Elevated grass track in Nuremberg at the Frankenstrasse station , 2012
Elevated grass track, Freiburg i. Br.
Elevated grass track with lateral filling stones, Nordhausen
Low-lying grass track with Vignole rails, Cologne
Detail: grooved rail embedded in grass
Track with ground cover, Zwickau
Alicante, high-lying grass tracks with Vignole rails
Chemnitz, Reitbahnstrasse; high grass tracks with Vignole rails, grooved rails were only laid in the switch area.
Zwickauer Strasse (Leipzig), deep grass track under construction. The track beams rest on support points and form two adjacent underground bridges per track. The track position is regulated by elastic inserts between the track beams and sleepers; regular tamping is neither necessary nor possible.
The rails are covered during filling. ( Strasbourg tramway )