Rail operator SMRT has identified the root causes of some of the technical glitches which have been affecting the North-South Line in recent weeks.

SMRT Trains' chief executive officer Lee Ling Wee revealed this in a company blog this week.

Mr Lee said the discovery was made after joint investigations with the Land Transport Authority (LTA) and signalling system supplier Thales. He said SMRT is working around the glitches "while waiting for software fixes to be implemented by Thales".

"We are planning a software patch in the coming weeks," he wrote. "We are hoping for a smooth implementation."

A software patch is a piece of software designed to update a computer program to fix or improve it.

Mr Lee described the whole procedure as "tedious".

"No two railway systems are identical in the way they are designed and operated," he explained. "The system hardware and software we have are customised for the unique local environment.

"While the system supplier had experience working with other operators in the world, they are unable to simply replicate the well-oiled systems of Taipei, Hong Kong and London, and import those here."

The Straits Times understands that it is the first time Thales is implementing the new signalling system - which allows trains to run at a higher frequency and without drivers - on a viaduct exposed to the elements.

Software had to be tweaked to take into account wet-weather braking, for instance.

Despite the discovery of "root causes" and imminent software patching work, Mr Lee made no commitment on when the new signalling system would settle down.

But in May, the LTA said it would take up to six months - or up to November.

That, however, is not the end of the tunnel for commuters. The same signalling project is also being carried out on the East-West Line. When that is completed next year, several more months of teething issues are expected.

Commuters have had to deal not only with the resignalling glitches, but also with a spate of unrelated faults. These include a power fault which brought trains to a halt on both lines on Wednesday at midnight for about 20 minutes, and two separate faults which affected service on the East-West Line for two hours during Wednesday's morning rush hour.

Singapore Institute of Technology assistant professor (engineering cluster) Andrew Ng said that while "teething issues are inevitable" on the new signalling system, more could be done to help commuters besides bus bridging services. He said the operator and regulator may consider "discounted fares, or even free pre- peak travel, on affected lines to soothe frayed nerves".

Commuter Jon Yeo agreed. The 48-year-old bank officer, who has been affected by several recent incidents, said free buses should be offered throughout the affected line until the system faults are resolved.

To expect commuters to bear with the episodes for a few more months "is unfair to both commuters and employers", he said, pointing to the productivity lost in each incident.

National University of Singapore transport researcher Lee Der- Horng acknowledged that it is a difficult project.

"But because of the complexity involved, they should have also foreseen the hiccups and paid more vigilance.

"From the commuter's angle, any service disruption will always be hard to swallow," he said, especially since one does not know when it will strike.