In an unusual move, prosecutors had to engage an expert to estimate the alcohol content a motorist had in his breath when his car ploughed into a 61-year-old rag-and-bone collector, killing her.

Although Tibrewal Sunil Kumar, 48, initially failed a breathalyser test when the police tested him at the scene of the accident on Feb 20, 2016, a second analysis found that he had 32 microgrammes of alcohol in every 100ml of breath - three microgrammes under the limit.

It emerged in court that it was two hours and 40 minutes following the accident that the second test was administered at the Traffic Police headquarters in Ubi Avenue 3, after the Indian national was arrested. Court documents did not state the reason for the delay.

About five months after he was charged in November 2016, the prosecution team engaged Dr Yao Yi Ju, divisional director of the Analytical Toxicology Division of the Health Sciences Authority.

She estimated that Tibrewal, a Singapore permanent resident, had between 42 and 58 microgrammes of alcohol in every 100ml of breath at the time of the accident.

Tibrewal was yesterday sentenced to 10 months' jail and disqualified from driving all classes of vehicles for eight years, for causing the death of Madam Tan Powi Kim, by committing a rash act.

One count each of drink driving and causing grievous hurt to her husband, Mr Cheng Kiat Yan, 69, by committing a rash act, were considered during sentencing.

Deputy Public Prosecutor Li Yihong said the accident happened after a drinking session that lasted about nine hours.

Tibrewal had left Orchard Towers with a colleague at around 6.20am and was driving his black BMW along Collyer Quay towards Esplanade Drive about 40 minutes later when he started feeling sleepy.

Tibrewal, then vice-president of a firm here dealing with shipping vessels, was negotiating a bend when he took his eyes off the road and removed one hand from the steering wheel to wake his colleague.

As a result of this rash act, his car swerved towards the extreme left lane of the four-lane road and hit Madam Tan, who was standing at the rear of her stationary lorry. She was flung onto the roof of the car before landing on its bonnet, while her husband fell onto the road.

Madam Tan was pronounced dead in hospital about an hour later. Mr Cheng's injuries included a fracture in his left knee.

Tibrewal is appealing the sentence.