*3.1.2 Rail maintenance*

Similar to the ballast maintenance, we can analyze the rail maintenance in more detail using the damage function according to Section 2, the damage mechanism D4 for both rail surface damage in wider curves and rail side wear in tighter curves. Note: Rail grinding in tangent track is not assessed, as this is driven by the damage functions D2 and D3.

Differently to ballast maintenance, regional passenger trains contribute significantly to both rail surface damage and rail side wear (**Table 15**). Again, doubling the transport volume (and thus the rail maintenance following the gross-ton-approach) by increasing one market segment only, we see distinct differences.

This result is not linked to train speeds, but mainly to the vehicles in use. Rail maintenance is mainly driven by the type of bogie and the longitudinal stiffness of the car body. Therefore, we need to look deeper into different vehicles.

### **3.2 The influence of vehicle properties on track maintenance**

As shown in Section 2, the alternative description of track loading as specific damage goes along with vehicle properties such as axle load, unsprung mass, traction power or longitudinal stiffness and also for some damage mechanisms with vehicle

speed. Since the total damage is calculated as a sum of those impacts, it is in turn also possible to allocate track maintenance to single vehicles. This chapter gives examples for the influence of different vehicle properties in combination with operational scenarios. In order to sum up different track maintenance works, for this task, we use the maintenance costs. Thus, the following results are track maintenance cost per vehicle-kilometer, sometimes re-calculated to track maintenance cost per gross-tonkilometer. As the absolute cost level varies from infrastructure manager to infrastructure manager and are moreover not of importance for this investigation, the costs are normalized. The 100% base level is a fully laden 4-axle freight car with Y25-bogies (axle load 20.5 tons) running at 90 kmph on a straight track. The track is according to the network configuration in Section 3.1 a ballasted concrete sleeper track on good subsoil with 60E1-R260 rails. Note: In order to keep results comprehensible, we do not add any costs of turnouts so that the damage mechanisms D5 and D6 are not added. Also, D7 is not addressed as we model track maintenance only, without incorporating renewals.

To better understand the results, it is essential to know the track maintenance expenses allocated to the damage mechanisms. According to the network configuration and the superstructure parameters, track maintenance costs split into the percentages displayed in **Figure 3**. We see that the overwhelming part of the costs (85%) is triggered by the damage mechanism D1, the dynamic vertical forces. These costs

**Figure 3.** *Track maintenance expenses.*

#### **Figure 4.**

*Track maintenance costs per vehicle-kilometer—4ax-Y25 freight wagon\_20 t.*

contain mainly ballast-related maintenance and small reactive maintenance. In this network, some 12% of track maintenance costs are due to rail surface damage (D2, D3 and D4.1) and thus rail grinding or milling costs. Only 2% of the costs are the consequence of rail side wear in curves.

Looking at the reference vehicle (**Figure 4**), the heavy freight car, we learn that ballast-related maintenance costs increase with decreasing track radius. Moreover, rail surface maintenance costs in straight tracks are very low and increase with decreasing track radius to be finally replaced by rail exchange costs (rail wear) in the smallest radius (250 m).

Locomotives and generally powered axles come along with higher unsprung masses and in addition with traction forces. The latter deliver a significant contribution to the rail surface damage in straight sections (damage D3). **Figure 5** shows both

**Figure 5.** *Track maintenance costs per vehicle-kilometer—Powered and unpowered axles.*

effects directly compared to the unpowered axles of the freight wagon. Both vehicles have the same tonnage but contribute very differently to the track maintenance needs. This is in accordance with [16]. The third column shows the influence of speed: Due to the high additional dynamic forces, the allocated track maintenance costs double when operating the same loco at 160 kmph instead of 90 kmph.

The high differences between the allocated maintenance costs in straight and curved track originate mainly in the maintenance needs themselves. Track maintenance in tight curves reaches much higher levels than in straight sections (see [1]). In a network, curves form only a small part. Looking at the network used in this paper as reference (**Table 6**), only 24% of the track show radii below 1000 m. The wear formula allows for calculating associated track maintenance costs as a consequence of track radius and speed level. For this example, we use nine different operational situations (four radii classes and five speed levels according to **Table 6**). In our simplified example, all vehicles run along all lines exactly in the distribution of these operational situations. Thus, we can calculate the average track maintenance cost per average vehicle-kilometer (vehicles according to **Table 9**) and sum up how the single vehicles to trains deliver results as shown in **Figure 6**.

These trains have different weights and cannot be compared directly. This counts especially for the light electrical multiple units and the heavy freight trains. We thus re-calculate the train costs to gross-ton-kilometers, simply by dividing by the train weight (see **Table 9**). **Figure 7** shows the damage impact of one gross-ton-kilometer on the track: Again, the long-distance passenger train is the 100% level. The regional trainsets deliver 20 to 40% less track damage. This is due to the lighter axles, less unsprung masses and the lower speeds compared to the fast intercity-train. The freight train has similar axle loads on average compared to the long-distance passenger train and the same loco, but runs at 100 kmph maximum so that the impact per grosston-km is 31% lower. **Figure 7** also shows the gross-ton-kilometer approach with the dashed light gray bars: In this approach, all these trains are meant to cause the same track damage.

These first examples compare very different trains and/or vehicles. It is not surprising that the track damage caused by these vehicles differ widely. But these differences occur for similar vehicles in the same way. We looked at locos with similar total weights (which is always close to the maximum allowed weight of 90 tons), but very

**Figure 6.**

*Track maintenance costs per train-kilometer for different trains.*

#### **Figure 7.**

*Track maintenance costs per gross-ton-kilometer for different trains.*

differing unsprung masses, and bogie stiffnesses. In **Figure 8**, we see differences up to 65% for operating the locos on passenger trains with speeds up to 160 kmph in the artificial network. In freight operation, the differences are much lower, 20% maximum.

From a track maintenance point of view, the use of track-friendly vehicles is of course preferable. However, the selection of vehicles or even train concepts focuses on many other aspects. We highlight the use of different train concepts as our next example: As an alternative choice for the long-distance passenger train consisting of the loco and seven wagons, an electrical multiple unit enabling higher speeds is analyzed. This trainset comes along with distributed powered axles, comparably high axles loads as the trainset is a double-decked unit and a total weight of some 400 tons. In **Figure 9**, we see three different options for performing a comparison. The red line demonstrates the allocated track maintenance costs of the loco hauled passenger train for the different radii and speed ranges (100% is the cost at speed level S5, 150 kmph).

**Figure 8.** *Track maintenance costs per gross-ton-kilometer for different locos.*

#### **Figure 9.**

*Track maintenance costs per gross-ton-kilometer for different long-distance passenger trains.*

This red line is the same for all three comparisons. Initially, we look at the track maintenance cost per vehicle-kilometer (black solid line). The EMU causes some 20% lower damage in curves, only slightly lower damage in straight sections with moderate speeds, and only at the highest speed (velocity range 5) higher track maintenance cost (plus 9%). As the trainset is lighter than the push/pull train, we again re-calculate the cost to gross-ton-level (dashed black line). We learn that the impact of these two trains is very similar on gross-ton-level; in the highest speed range the inserted damage of the EMU is 30% higher. The third possibility for comparing different passenger train configurations is to refer the track maintenance cost caused to seatkilometers. In this option, the double-decked trainset option performs best: As the dotted line in **Figure 9** indicates, the difference is remarkable and reaches values up to 35% less track maintenance costs caused.

**Figure 10.**

*Track maintenance costs per vehicle-kilometer—4ax-Y25 freight wagon\_20 t with varying track components.*

*Traffic Load and Its Impact on Track Maintenance DOI: http://dx.doi.org/10.5772/intechopen.110800*

Concluding, we want to underline that not only loading triggers track maintenance. Improving track structure and installing innovative, robust components helps to drop the maintenance demands—much more than track-friendly vehicle concepts. **Figure 10** shows, for example, the impact of using concrete sleepers with under sleeper pads [31, 32] on the ballast-related maintenance costs (dashed yellowish bars) and on top, for example, a rail steel grade of R350HT in curves (dashed purple bars—rail grinding and rail exchange). The track maintenance cost decreases by more than 40% using these components in curves and still by one third in straight sections where higher rail steel grades do not reduce maintenance demands.
