The Straits Times understands that the cracks, which appeared near the ongoing construction site of the Bukit Brown road, were caused by an unexplained subterranean heaving of the earth. The Land Transport Authority (LTA), in updates on Twitter, had advised motorists to avoid the affected stretch.

In a statement, LTA said the it discovered the cracks at 8:00am along a stretch of Adam Road after the MacRitchie Flyover. "Two out of four lanes were immediately closed to facilitate repairs," a spokesman said, adding that all lanes were re-opened at about 10:00am, 'after we ascertained that the road is safe for use'. The widespread congestion however, was still apparent well past 10:30am.

The LTA said it was investigating the cause of the incident. A civil engineer who declined to be named said the cracks were likely to have been caused by soil movements below the road related to nearby construction works. He said the rain might have contributed to the 'loss of ground... by draining away soil, thereby weakening the site'.