Network Rail: Assets
The question
To ask the Secretary of State for Transport, pursuant to the Answer of 14 January 2026 to Question 102105 on Network Rail: Assets, what assessment she has made of the effectiveness of Network Rail’s calculation of the Composite Sustainability index for each railway asset; and what assessment she has made of rail asset (a) age and (b) condition in (i) Control Period 4 (ii) Control Period 5 (iii) Control Period 6 and (iv) Control Period 7.
Answered by Keir Mather
The methodology for the composite sustainability index (CSI) calculations is developed by Network Rail and is recognised by the regulator, the Office of Rail and Road, as being a reliable and effective means to monitor the changing remaining life of railway infrastructure.
Rail asset age and condition, as determined via CSI and service affecting failures (SAFs) respectively, are shown in Table 1 and Table 2.
Table 1: CSI shift across Control Periods
| CP5 exit | CP6 exit | CP7 Y2 update |
CSI shift against a baseline of the start of CP5 | 0.40% | -1.20% | -2.60% |
Table 2: SAF shift across Control Periods
| End CP4 | End CP5 | End CP6 | Latest 13 Periods in CP7 |
SAFs per year | 28,914 | 24,711 | 23,339 | 23,025 |
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