*Assessing Average Maintenance Frequencies and Service Lives of Railway Tracks:… DOI: http://dx.doi.org/10.5772/intechopen.110488*

**Figure 9.** *Rail grinding over track radius.*

**Figure 10.** *Rail exchange over track radius.*

**Figure 11.** *Rail grinding over track radius for different steel grades.*

radius for different rail steel grades. As rails with higher steel grades come along with slightly higher investment costs only, the savings in maintenance pay back at least for high transport volumes generally.

**Figure 12.** *Rail exchange over track radius for different steel grades.*

#### **3.3 Network-wide maintenance and renewal demand**

Having described the average maintenance frequencies and the service lives as a consequence of varying boundary conditions, we can also calculate network-wide demands on this basis. This is important to guarantee sufficient budgets in order to achieve sustainable network quality and the economic optimum. The positive influence of higher-quality of track components and improved subsoil can also be depicted on this aggregated level. Of course, in a network, it takes time until all track sections are equipped with the most sustainable components, but at least such evaluations can highlight the goal and support the implementation.

The following evaluations are performed for an artificial mixed traffic network of 10,000 kilometers. The network consists of 76 percent of straight tracks (R > 1000 m), 12.5 percent of 600 m < R < 1000 m sections, 6.5 percent of tracks with radii between 400 and 600 meters, 4.5 percent of radii in the 250 m < R < 400 m class, and 0.5 percent sharp curves below 250 meters. The track loading is fixed to 10 to 15 million gross-tons per year, summing up to 125 <sup>10</sup><sup>6</sup> gross-ton kilometers per year. In the basic scenario, the tracks consist of concrete sleepers with 60E1 rails with standard steel grade R260 on medium ballast and good subsoil and good drainage conditions.

This configuration leads, according to the referring Standard Elements, to a maintenance demand of 1747 km of tamping, 504 km of rail grinding, 5.6 km of rail exchange, and a renewal demand of 283 km which is equivalent to an average service life of 35.3 years.

If we look at the ballast-related maintenance and the renewal demand for different ballast and sleeper types, and varying subsoil and drainage conditions, we can see the high importance of high-quality components (**Table 2**): perfect ballast helps reducing the tamping demand by 40 percent and renewal demand by 30 percent, while poor ballast in contrary leads to m a more the double tamping demand, additional ballast cleaning needs and nevertheless to a 50 percent increased renewal demand. Moving from standard concrete sleepers to padded sleepers helps to achieve similar benefits than good ballast quality, almost 30 percent reduction of yearly renewals, and only half of the tamping demand.

The condition of subsoil and drainage is crucial. Facing poor dewatering conditions can easily increase the tamping demand by one-third, poor subsoil even by 100

*Assessing Average Maintenance Frequencies and Service Lives of Railway Tracks:… DOI: http://dx.doi.org/10.5772/intechopen.110488*


#### **Table 2.**

*Maintenance and renewal demand for different track structures.*

percent, and additionally costly ballast cleaning. Having both poor subsoil and poor drainage means doubled tamping demand (and some 2 percent of the network yearly ballast cleaned) and a doubled renewal demand. In this case and considering the transport volume, one-third of the network needs to be tamped every year and 5.7 percent of the track require track renewal.

For rail maintenance, the rail steel grade is a game changer: For the given loading of 10 to 15 mio. Gross-tons and a superstructure with concrete sleepers on medium ballast with good subsoil and drainage condition, rail grinding demand can be reduced by up to 40 percent using heat treated rails. The side wear-driven rail exchange (including the necessary exchange of the inner rail every second to third exchange) drops to 20 percent in the case of rails R350HT, to almost 0 in the case of a steel grade of R400HT (**Table 3**).

In extended mixed traffic networks, we find a mixture of these parameter values and tracks with different ages. Some—low—percentages of the networks might face any poor subsoil conditions. Ballast might be better or worse in different parts of the network or in different lines. We find different rail profiles, rail steel grades, and sleeper types. If assessing realistic samples of existing networks, it turns out that following a high-quality strategy has the potential of a 50 percent reduction of yearly maintenance expenses and up to one-third of renewal costs per year. Of course, the first step is to invest in more robust components and improved subsoil. This comes


**Table 3.**

*Rail maintenance for different rail steel-grades.*

not for free but pays back in the long term. Economic evaluation is not the topic of this paper but is well-published [24, 25].

As shown, the Standard Element Approach allows for predicting future demand of track work, maintenance as well as track renewal. The following examples show the net wide effects of implementing innovation. The calculation is executed on a fictive network. Different innovative track components prolonging the service life are modeled. Furthermore, an increase in the transport volume of annual 2.5 percent is assumed. Starting at **Figure 13**, we see the forecast of track renewal assuming that transport volume is constant and tracks are re-built with the same components and on unchanged subsoil condition. The five renewal waves (in different colors in **Figure 13**) smooth out over the long term to a somewhat constant renewal demand.

If following the strategy to re-invest tracks always with the optimal component mix and to rehab subsoil in case it is necessary, the renewal demand decreases after the first renewal wave. The prolongation of service lives (e.g., due to padded concrete sleepers plus 25 percent [26, 27] stretches the necessary renewals in the future (**Figure 14**).

Considering an increase in transport volume, in this example by 2.5 percent per year, track sections move from one loading class to the next higher one. This goes

**Figure 13.**

**Figure 14.**

*Re-investment demand for several service lives with replacement of strategic components.*

*Assessing Average Maintenance Frequencies and Service Lives of Railway Tracks:… DOI: http://dx.doi.org/10.5772/intechopen.110488*

#### **Figure 15.**

*Re-investment demand for several service lives with replacement of strategic components for rising transport volume.*

along with decreasing service life and early renewal of course. Again, this process impacts the renewal demand in the long term only (**Figure 15**), but we see that it shifts the necessary track re-investments to the level displayed in **Figure 13**. We learn that further improving track components in order to increase the total service life of the track is not only to reduce maintenance in the short and mid term but to keep networks with growing transport volume in a balanced state.

This example underlines that Standard Elements form sound knowledge which can be used for various analyses and evaluations.
