While the estimated lifespan of rail assets provide a guide as to when they need to be replaced, these typically deteriorate at different rates and are changed on an ad-hoc basis, Transport Minister Lui Tuck Yew said yesterday.
Using the example of timber sleepers, he told Parliament that while two different sets were used, those which were installed later actually wore out more quickly. This is because of factors such as the type of wood used and how the wood was treated.
He was responding to Workers' Party Non-Constituency MP Gerald Giam, who asked if the replacement of rail assets was done on a timely basis in the light of the July 7 peak-hour breakdown of the North-South and East-West Lines.
Timber sleepers are used to hold train tracks in place.
Mr Giam said the website of rail operator SMRT indicated that sleepers last between 15 and 25 years. This meant replacement works should have been completed by 2002 or 2012, given that the MRT started operations in 1987.
But he said the SMRT started doing so only in November 2012.
Responding, Mr Lui said that "the important thing is actually to monitor them on a consistent level (and) replace them on an ad-hoc basis as and when necessary".
"But when it reaches what is considered a critical threshold, then you want to consider changing them out, replacing them en masse. And in this case, we are doing so with concrete sleepers."
Upgrading of track components also had to be prioritised. For example, replacement of the third-rail, which supplies power to the trains, faced a "slight delay" and could be completed only by 2017.
This is because there is a need to "de-conflict" works that are ongoing, such as replacing sleepers and upgrading the signalling system.
Separately, Mr Giam also asked if it was the responsibility of the Land Transport Authority (LTA) or the operators to initiate asset renewal, and if there were any conflicts between the LTA and SMRT.
Mr Lui said it was the operator's responsibility as it has the best idea of the condition of components.
He added that a "certain healthy tension" is to be expected between the two parties because the regulator does the audits and provides feedback to the operator to take certain actions.
He said that joint teams report to him every three months, and the LTA has stepped up planned and surprise audits on operators, and even embedded an audit team in SMRT itself.
Mr Giam, in another query, asked Mr Lui if he agreed that "a lot of these replacement works should have actually started earlier, pre-2012, in order to be able to complete... before the end of life of the system?"
Said Mr Lui: "I think it's not always clear when the end of life is. There may be an estimate given but, because of varying conditions, that can always change. And in any case I suspect that perfect foresight is as rare as 20/20 hindsight is common."
