Even as a High Court judge set a new three-tier sentencing framework for those who cause grievous hurt due to negligence on the road, he questioned an appellant's use of an MP's letter to downplay her culpability.

According to the letter, Tang Ling Lee, whose appeal against a one-week jail term for colliding with a 27-year-old motorcyclist was eventually dismissed, had only "accidentally brushed a motorcyclist resulting in the motorcyclist sustaining some injuries".

But Justice See Kee Oon highlighted that this was not consistent with the statement of facts she had agreed to. The victim, Mr Vikaramen A. Elangovan, suffered multiple fractures requiring a dozen operations in two months, and was hospitalised for 69 days after he was hit by the car she had been driving.

"These statements are regrettably misleading if they correctly reflect what she had conveyed to the MP," said the judge in decision grounds issued last week.

Tang, 45, had been sentenced to one week in jail and banned from driving for two years last year after she admitted that on Sept 16, 2016, she had failed to keep a proper lookout while making a right turn at a junction in Ang Mo Kio.

Appealing against the jail term, her lawyer Adrian Tan Wen Cheng argued that a fine would have been sufficient. But Deputy Public Prosecutor Houston Johannus objected, pointing to Tang's high culpability and the "substantial harm" caused.

The judge noted that past cases show the same offence had resulted in a fine in some cases but jail in others. Saying it "would be useful to provide some guidance... which might help foster more consistency", he included in his judgment a three-tier punishment framework based on the degree of harm and culpability for cases in which a trial is claimed.

In the most serious of traffic accident cases, involving "greater harm and higher culpability", the presumptive sentencing range will be more than two weeks in prison. At the lowest end of "lesser harm and lower culpability", fines would be enough. For cases which fall in between, he prescribed one to two weeks in jail.

While video footage from her car's camera showed she had not been speeding, she had not stopped at the junction at all and had swerved fairly abruptly, "barely seconds before the motorcyclist was about to cross the junction as well". The judge decided that either her attention was diverted elsewhere or she had exercised appallingly poor judgment.

The judge also highlighted factors which increase culpability, such as "speeding, drink-driving, sleepy driving... driving while using a mobile phone... driving against the flow of traffic or off the road" as well as driving without a licence or while under disqualification.

Those behind the wheel should also take greater care when driving during rush hour, within a residential or school zone, or when driving a heavy vehicle.

Justice See found that Tang's case fell in the most serious band, which meant more than two weeks' jail.

While video footage from her car's camera showed she had not been speeding, she had not stopped at the junction at all and had swerved fairly abruptly, "barely seconds before the motorcyclist was about to cross the junction as well".

The judge decided that either her attention was diverted elsewhere or she had exercised appallingly poor judgment.

He dismissed her claim that she had mistaken the motorcycle's headlight for a street light.

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Still, her guilty plea, remorse shown, clean record of 20 years and the fact that she stopped to help the victim, justified reducing the sentence to one week in prison, the judge added.

At the close of his written judgment, Justice See described her use of the MP's letter as "somewhat troubling" given that the statements within "sought to unfairly trivialise the accident and diminish the true extent of the victim's substantial injuries".

It was not stated in his judgment which MP sent the letter on Tang's behalf to the State Courts.