A massive 12-hour operation was mounted to clean up and repave part of Bukit Timah Expressway after an oil spill which caused southbound traffic to grind to a halt through much of the morning.
By yesterday evening, rush-hour traffic was back to normal.
But for thousands of morning commuters, the oil which had leaked from a Malaysian-registered palm-oil tanker just after the Mandai exit meant massive jams, with traffic backing up into the heart of Woodlands more than 3km away.
The congestion even held up more than 10 bus services departing from the Woodlands Regional Bus Interchange for more than two hours.
Drivers looking to detour around the jam were also hit, as the gridlock rippled to surrounding routes, such as Mandai Road and Gambas Avenue. Commuters went online to vent their frustrations, putting up photos and videos of the jam.
Mr Vincent Lee, 26, who was travelling by bus along Woodlands Avenue 3 to his workplace in Woodlands Centre Road, said: "I have never seen traffic so bad..."
The traffic snarl started to ease only around 3.15pm, when the Land Transport Authority (LTA) opened one of two lanes that had to be resurfaced, nearly 12 hours after the accident which eventually led to oil spilling on the expressway. The other lane was opened at 6.35pm.
The police and the Singapore Civil Defence Force (SCDF) told The Straits Times that they were alerted to the incident at around 3am and that a 41-year-old man was taken conscious to Khoo Teck Puat Hospital from the scene.
The man had driven into the back of a Malaysian-registered oil tanker, crushing the entire hood of his car.
The SCDF said initial on-site investigations did not identify any oil spillage. But three hours later at 6.07am, it received another call, this time about a resulting oil spill from the accident, and dispatched two fire engines.
The tanker's 52-year-old driver, Mr Nazib, claimed that his tanker, which was carrying 29 tonnes of oil, had been damaged by the collision and had started leaking at the rear. The two leftmost lanes were closed by the LTA at around 6am to allow for cleanup works, which forced traffic to a standstill.
The National Environment Agency (NEA) told The Straits Times that workers were deployed to the scene at 6.15am to assess and assist.
"The palm oil spill was extensive, requiring the deployment of oil absorbent pads and oil booms to contain the spread of the spill," said an NEA spokesman. The NEA added that the clean-up was completed at about 1pm. The LTA also had to resurface an approximately 80m stretch of the affected roads.
About 10 workers were seen soaking up the oil with absorbent pads and shovelling dried oil from the ground when The Straits Times visited the site at noon. Even then, oil was still leaking from the truck's rear and workers were seen collecting it in barrels.
By then, yellow oil had flowed between the grills of the drains on the left of the expressway and down into the drains below. The Straits Times understands that the drains do not lead to any reservoirs, so the incident should not have affected the country's water supply.
Last January, a stretch of Paterson Road near Orchard Road was closed for 13 hours after an oil spill caused by a leak from a truck. It led to a massive tailback on roads feeding into the area. The stretch on Paterson Road heading towards River Valley also had to be resurfaced.
• Additional reporting by Dominic Teo, Lim Yi Han and Alphonsus Chern