SINGAPORE — The cracks across two lanes of Adam Road that caused a traffic snarl on Friday morning (June 1) were caused by rainwater that had seeped under the road, said the Land Transport Authority (LTA).

The cracks were not caused by nearby constructions works and do not pose any structural risks, it said.

The rainwater caused pressure under the base of the road to build up and a temporary section of the road to “heave”, resulting in the cracks, said the LTA on Friday evening as it announced the completion of its investigations.

The affected stretch of the road, towards Queensway, is a temporary section that was diverted to facilitate the construction of Lornie Highway.

Beneath the bitumen surface, temporary roads consist of softer materials than permanent roads. The sub-surface of temporary roads consists of reinforced concrete slabs, steel plates and high-density extruded polystyrene, while the sub-surface of permanent roads consists of materials such as stones, recycled concrete and slag.

The LTA said it detected the cracks at 8am and the affected lanes were closed for repairs. Workers drained the water under the road base and determined that it was safe before the LTA re-opened the lanes at about 9.55am.

To prevent similar incidents going forward, the LTA said its contractor for the Lornie Highway project, Swee Hong, will ensure water is drained at all times to reduce the risk of water accumulating at the side of the roads.

Earlier in the day, two of the four lanes of the road were closed for repairs.

Traffic was smooth by the time TODAY arrived at the scene slightly after 10am.

The cracks, which appeared bigger in photos being shared on social media, had been narrowed and were barely visible.

The affected site was beside a construction site that was located in the middle of Lornie Road, just before the entrance to the Pan Island Expressway.

Earlier on Friday morning, social media users complained of being stuck in traffic, due to the cracks and the heavy rain.

In a tweet around 10am, the LTA wrote: "Heavy Traffic on Adam Road (towards Queensway) after MacRitchie viaduct".

Just before 11am, bus operator SBS Transit said in a tweet that bus services plying Lornie road were "back to normal". Earlier, it said there were delays due to "urgent road works".

One motorist, who only wanted to be known as Mrs Lee, was driving to Dover Road when she got caught up in the jam slightly before 8am.

The 44-year-old homemaker said that as she got closer to the site where the cracks appeared, she noticed traffic cones had been set up. She also saw three workers from the construction site directing traffic to an unaffected lane.

While she did not see the cracks, she felt her car going over them when she filtered lanes to avoid the traffic cones.

Estimating the cracks to be around 20cm in height, Mrs Lee, who later returned to the site at around 11am to find out what had caused the incident, told TODAY: "It wasn't like going over a speed hump…it felt like I was going up a multi-storey carpark ramp."

Workers from the construction site declined to comment on the incident.