Difference Full and Temporary Failure Recovery

The failure recovery at ProRail consists out of multiple types. This type indicates the degree of recovery of the functionality of the infra. ProRail makes use of four different failure recovery types displayed in Table I.1. As can be seen from the table, a full failure recovery is by far the most occurring failure recovery type, followed by temporary failure recovery.

Table I.1: The Types of Failure Recovery applied on Urgent Failures and their Occurrence.

Type Failure Recovery

Work done by Contractor Example Status Infra- Object

Occurrence

Full

Recovery The contractor finished the failure recovery process Level crossing barrier (“overweg-boom”) replaced. Object functions for 100% 71.2% Temporary Recovery

The contractor used a temporary solution to make the object function again. He has to come back at a later date.

Level crossing barrier of another type placed (only spare part available). Correct barrier is placed later. Object functions for 100% 16.5% Partial Recovery

The contractor used a failure recovery method which only partially solves the problem. He has to come back at a later date.

Switch fixed in place. Only one direction of path is usable.

Object functions partially

2.7%

No Recovery The contractor did his research but not any failure recovery work.

As soon as the mechanic arrived at the failed switch, the switch started working again. It still worked after half an hour thus the mechanic left.

Object functions for 100% / Object does not function 9.6%

Since a temporary failure recovery is executed for different reasons and under different

circumstances than a full failure recovery, a different distribution of failure occurrences over the failure forms can be expected. As shown by Figure I.1, this is indeed the case. The failure forms are plotted in the pie chart in the same order as they were plotted as in the pie chart of Figure 4.1, which is in the order of frequent occurrence when a full recovery is executed. The figure shows that a temporary failure recovery tends to be especially more frequent for path TOBS and level crossing failures.

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Figure I.1: The Percentage of Temporary Failure Recoveries of a Specific Failure Form as compared to the Total Amount of Occurrences.

This increase in frequency can be explained by a look into the motivation for temporary failure recovery instead of a full recovery. A common situation when temporary failure recovery takes place is when the spare part is not present but the failure has to be repaired. Instead of waiting a long time for the spare part to be recovered, another, less suitable, part is used (like in the example in Table I.1). Another typical temporary solution is the placement of a “slipkabel”. This is a cable which is placed to replace the energy supply of another, possibly failed, cable. It is often not clear where in this cable the failure is. It is also possible that, if the cable failure is located, repairing the failure takes too much time. For these cases, it can be more attractive to place a temporary, replacing slipkabel to get the energy supply up and working again.

When analysing the temporary failure data, three types of motivations to execute a temporary instead of a full failure recovery are found. Each of these results in a different kind of question to be asked:

 75% of the temporary failure recoveries are executed because of the faster solution they offer to the problem. Thus, the problem is known and the mechanic makes, in

consultation with the Trdl, the decision to execute a faster, temporary failure recovery based on the expected repair time and the necessity to use the path at the current moment. It is important to compare the repair times (thus, without the diagnosis time) of a temporary failure recovery with a full failure recovery in this case. This helps the mechanic and the Trdl to make the right decision about the type of failure recovery to execute. 35.5% 10.5% 17.8% 9.8% 3.3% 5.1% 1.8% 6.9% 1.1% 1.1% 2.2% 0% 1% 0.7% 0.4% 0% 0.7% 0.4% 2% 0% 0%

0%

Failure Forms

Switch NIC [2]

Level Crossing Disturbed [3] Level Crossing Collision [4] Switch TOBS [5]

Sign Irregular [6]

Level Crossing Barrier not Responding Properly [7] Other Failures [8]

Path Subsidence [9] Switch Disturbed [10] Status Path, Others [11]

Level Crossing Specific Damage [12] Kink in Path [13]

Sign Turned Off [14] Smouldering Sleepers [15] Level Crossing TOBS [16] Bridge Disturbed [17] Overpass Collision [18] Switch Specific Damage [19] ATB-System Failure [20] Fire [21]

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 19% is executed because there is no spare part present. Like in the example of Table I.1, a different type of spare part or even the old, partially repaired, part is used. The only way to directly execute a full failure recovery would be to wait for the spare part to arrive. In this case, whether or not this waiting time is worth it is the most important consideration.

 The last 6% of the temporary failure recoveries are executed because the direct cause of the failure could not be found, but this temporary solution would surely solve it for now (like a long slipkabel when the exact failure location in the cable has not been found yet). The question to be asked here is whether or not to spend more time to search for the exact cause. However, since this motivation only represents a low amount of the failures and the marginal value added when looking longer is expected to be low, the assumption is made that the mechanic and the Trdl make the right call in this case.