Higher and higher rail traffic speeds have led to progressively more problems associated with the conventional railway design with a ballasted track. In the high-speed railway networks of Germany and other European countries the conventional ballasted track as a long-established, tried-and-tested system has reached its physical limits and is no longer capable of meeting requirements such as minimal susceptibility to faults and low maintenance costs combined with close distance spacing and high track capacity and therefore has no long-term future.
As an alternative, in 1972 DB AG, scientific institutes and the construction industry developed the so-called fixed track construction style, “Rheda,” which together with the construction style, “Züblin,” has been approved as the standard track for high-speed sections of German Federal Railways since 1992. In fixed track systems, the track formation layer and the gravel ballast of the conventional ballasted track are replaced by a hydraulically bound subbase with an asphalt or concrete base course on top. The overall structure is regarded, and hence treated as a system—earthwork/concrete base course—that is to be statically dimensioned. In contrast to ballasted track, it is very rigid and computationally determinable. The basic idea in developing the fixed track is to guarantee a uniform resilient bedding for the track, this being achieved almost exclusively by resilient intermediate layers in the region of the rail fastening or by resilient sleeper support systems. As a result, even in the speed range above 200 km/h the track is supported uniformly and with lasting positional stability, which means that e.g. larger cambers and hence higher cornering speeds become possible but also that maintenance outlay is negligible compared to the conventional trackbed.
Fixed track systems are subdivided mainly into two construction styles or design principles: in the case of the first, concrete sleepers (also concrete-block and steel tie-bars) or support blocks are embedded in concrete and therefore connected to form a monolithic structure, the track grating having to be fitted and vibrated and/or bedded in with millimeter accuracy. Later, this was changed to mounting and anchoring the track gratings directly on an asphalt or concrete base plate, which in turn has to be done continuously with millimeter accuracy. This has the advantage—not provided by a monolithic style of construction—of enabling the exchange of the individual sleepers. Here, the individual suppliers of fixed track systems vary in terms of conceptions and detail solutions. There are currently seven selected systems being tested on an operating trial section between Mannheim and Karlsruhe, including systems without sleepers, where the rail has been fastened directly onto support points of the concrete base course.
While the fixed track system offers many incontestable advantages, it does of course also have drawbacks, some of them system-related. The main points of criticism are listed and explained below.
The Federal Audit Office has criticized the high cost of installing fixed track and pointed out that to break even financially with the conventional ballasted track a useful life of at least 60 years would have to be achieved. The counter-argument to this is that it is possible to eliminate measures such as screening, retamping and renovating old ballast sections that incur cost and disrupt rail traffic and therefore to increase the degree of utilization of the railways. Despite automation and prefabrication, it is impossible to push the cost of creating the existing conventional fixed track systems down to the level, or below the level, of ballasted track, although there are always attempts at optimization. The high capital outlay for creating fixed track systems is due to their more complex manufacture, which is also reflected in a much longer construction period. This arises from the need for very high accuracy when laying track gratings and/or installing base plates, the need for costly upgrading of the soil (except for tunnel construction), and the construction period interruptions entailed by hydraulically bound layers and troughs supported on and in one another. The fundamentally required preliminary work, referred to here as costly upgrading of the soil, specifically means an exchange of the soil to a depth of, at times, over 3.0 m and subsequent layer-by-layer incorporation and compaction of precisely mutually tuned functional base layers in order to achieve the requisite properties, such as elasticity, stability, load distribution, frost protection, drainage etc. This also means i.a. that the renovation and conversion of an existing double-tracked ballasted section to the fixed track system may be carried out normally only by totally closing both tracks owing to the dimensions and shape of the trench.
As the next specific problem, the increased emission of airborne noise caused by the rigid structure and the absence of noise absorption is cited in many sources. Measurements and calculations have resulted in an airborne noise level increase of at most 3 dB(A), which has led to the use of cost-intensive sound absorbers and other sound-absorbing measures at the surface and in the edge region of the fixed track.
As a final and not unimportant drawback of all previous fixed track systems, the limited adaptability of the rail fastening and rail position owing to the monolithic structure is cited. Because the rail fastening points are invariably fixed and the displaceability of the rails is therefore limited to a minimal value, thereby making it relatively impossible to modify or adapt the operating pattern, very high demands are placed on the planning and surveying and designing of the route and the rail track. In contrast to the ballasted construction style, therefore, both subsequent modifications of the rail position and minor alteration of the track route or enlargement of the camber as well as point installation etc., if they are possible at all, are possible only with an extremely high outlay.
In summary, it should be stressed that with the currently available fixed track systems high capital costs are incurred as a result of the following parameters:                very high planning outlay also with regard to long-term operational planning,        very high outlay for soil exchange according to requirements,        very high surveying outlay simultaneously with execution of construction work,        very high construction outlay owing to the need for extreme accuracy.        
What is more, conversion of an existing, heavily used section is not possible these days because of the need for total closure of both tracks and the long construction period.
USPTO Backgrounds
USPTO Backgrounds