Heavy rain led to cracks that appeared across two lanes of Adam Road during the morning rush hour yesterday, causing massive jams as far away as Upper Serangoon and Bartley.
The Land Transport Authority (LTA) said that the cracks, which developed next to a huge excavation for the construction of an underpass that will be part of the Bukit Brown road, were caused by water pressure that had built up because of heavy rain.
The LTA said it discovered the cracks at 8am. "Two out of four lanes were immediately closed to facilitate repairs," a spokesman said, adding that they were reopened at about 10am, "after we ascertained that the road is safe for use".
The congestion, however, was still apparent well past 10.30am. The traffic tailback stretched for up to 8km to Bartley Road.
Other roads such as Lorong Chuan, Upper Serangoon Road and Serangoon Avenue 1 were also affected.
According to Google Maps, city-bound traffic on the Central Expressway was also crawling at 10.25am, possibly contributed to by drivers who were avoiding the Lornie-Adam route.
However, traffic was soon back to normal and there was no major congestion reported during the evening rush hour.
After investigating, LTA issued a follow-up statement at around 6.40pm. It said heavy rain had led to water accumulating and seeping under the road base.
The built-up pressure from the water caused the road section "to heave, thus resulting in the cracks on the road surface".
It said the cracks were not caused by the nearby construction works and "do not pose any structural risks". Water under the road base has since been drained, it added.
When The Straits Times arrived at the scene at 10.30am, staff from PUB were spotted assessing the situation.
Motorist Aaron Hia, 33, was one of several thousands affected by the jam.
The product trainer with a motor distributor said he was more than an hour late for work.
"I called my boss to say I would be late, and apparently I wasn't the only one. Several others were late too."
Another motorist, who would give her name only as Ms Ong, said she left her home in Lorong Chuan at 7.30am and was very late for her 8am meeting with friends.
The 44-year-old housewife said: "The jam was terrible. My car was going up due to the uneven ground as I drove past the area with the cracks. It was very dangerous as no one knew what was going on. Fortunately, no one had an accident."
The construction of the new road - which LTA had called Lornie Highway - was delayed twice. Singapore-listed civil engineering group Swee Hong clinched the project in 2013 but it soon faced cash-flow problems, which led to the project dragging on.
The road was initially slated to be completed by mid-2016, but this was later extended to end-2017.
Last November, LTA said the road would be ready by the first quarter of next year - nearly three years behind schedule.
The 2km road cuts a swathe through the Bukit Brown Cemetery, considered by many to be a heritage site.
Besides Swee Hong's problems, the project was also held up by the exhumation of graves, which took almost a year longer than anticipated, LTA had said.
The Lornie Highway links the MacRitchie Viaduct to Adam Road via the 95-year-old cemetery.
LTA said the road was necessary to provide for future traffic, which is expected to increase by 20 per cent to 30 per cent by 2020.