A cab passenger who was fastening her seat belt as the vehicle was moving off will share the blame for the serious injuries she suffered when the taxi and another vehicle were involved in a collision just 20 seconds into the ride.

Dr Ishkawa Natsuko, 38, suffered skull, spinal and facial fractures and was taken to the Singapore General Hospital after the March 2012 accident. She stayed there for two weeks. The Singaporean is seeking compensation for medical expenses and treatment, loss of earnings and other items.

She accepted 15 per cent liability in a negligence suit she filed in the High Court against cabby Goh Peng Choon and the driver of the other vehicle. Vehicle insurers initially resisted her claims, saying she was to blame wholly or partly for not fastening the seat belt before setting off.

The novel case would help to settle the issue of when the liability to ensure seat belt use kicks in - when the car is stationary or when it is in motion.

Under the Road Traffic (Motor Vehicles, Wearing of Seat Belts) Rules 2011, the driver of a car has to ensure that every passenger is belted up, with some exceptions, such as medical cases.

All three witnesses testified on the first day of the trial earlier this year before Judicial Commissioner Foo Tuat Yien ended it the next day, when the parties agreed between themselves that they would apportion blame by mutual consent.

Dr Natsuko was fastening her seat belt after settling her things in the back seat when the collision took place, her lawyer Renuka Chettiar said in court papers.

It is understood that the parties inspected the route taken by the cab driver after picking up Dr Natsuko from Leonie Hill and making a right turn into River Valley Road, where the collision occurred.

Given that the cab did not speed off after picking her up and was slowed by the turn it made, it is believed there would have been time for Dr Natsuko to fasten the seat belt while the vehicle was moving, and this would have been factored into the deliberations.

Lawyer Anthony Wee, who defended Mr Goh on behalf of the vehicle insurers, said the other motorist had contributed to the collision by failing to keep a proper lookout.

Mr Christopher Fernandez, who represented the second defendant, Mr Low Ka Hoe, countered that the cabby was to blame for failing to give way when coming out of a minor road onto a major road.

As there were no local precedents in this area, it is understood that cases from abroad - which suggested a 10 per cent to 20 per cent contributory blame on the injured party - were considered.

In a 1975 English case, Lord Justice Alfred Denning ruled that if the injuries could be prevented altogether by the use of a seat belt, then the damages payable should be reduced by 25 per cent. If the failure to wear a seat belt made a considerable difference, then the damages should be cut by 15 per cent.

But if the injuries would have been the same if a seat belt had been worn, then the damages payable should not be reduced at all.

That case has been cited, with modifications, as a standard reference in several Commonwealth countries such as Australia and Canada. According to the judgment order issued by the judicial commissioner, both defendants agreed to bear 85 per cent of the damages payable to Dr Natsuko.

Of this 85 per cent liability, Mr Goh would bear 85 per cent of the share, while Mr Low would bear 15 per cent.

The case has now proceeded to assess the amount of damages payable to Dr Natsuko, who is seeking more than $300,000.

A High Court case-management conference was held last month.