SMRT said it has begun talks with the Land Transport Authority (LTA) on a complete overhaul of what it called an "ageing" rail network.
The operator added that its priority was the North-South Line, which has the oldest parts of the track. It was on this line that a rail crack delayed train services on Thursday for up to 40 minutes.
Preliminary investigations found that the latest problem was caused by corrosion, unlike two recent incidents on the same line which involved welded joints.
This, said SMRT's vice-president for corporate marketing and communications Kalai Natarajan, is "symptomatic of an ageing rail infrastructure". She warned that similar cracks can happen again.
"Engineers do not preclude similar incidents from happening in future," she said, adding that the rail infrastructure is experiencing the effects of wear and tear.
Before the three incidents, which happened in the space of five weeks, there was an average of only one rail crack per year.
SMRT is working with LTA to accelerate the replacement of the third rail system, which supplies power to trains. But it is also "critical" to look into changing portions of the running rail on which trains travel, which are almost 30 years old, Ms Natarajan said, adding: "This overhaul is seen as absolutely necessary for system safety and reliability moving forward."
It is believed additional replacement works could mean more planned closures on weekends.
When contacted, an LTA spokesman said the authority will "work closely with SMRT on the upgrading of the rail system".
After investigating Thursday's incident, engineers found that a corroded strip of metal in contact with the rail had caused the underside of the rail to weaken, and eventually crack. SMRT discovered the crack between Yio Chu Kang and Ang Mo Kio stations at 6.25am. It put clamps in place to stabilise the rail, and ordered trains to run more slowly along the affected track.
Ms Natarajan said that in this case, routine tests, including one which uses ultrasound, had failed to detect the defect as it had occurred under the rail.
She also noted that the latest rail crack is "markedly different" in nature from the previous two, as it occurred on a non-welded portion of the rail.
The previous cases, on April 29 and May 18, involved joints welded between old and new rails located on a curved track.
When asked what action SMRT would take to identify defects that could not be detected by ultrasound, she said visual checks would be stepped up across the entire network.
