A motorist who caused a crash which saw his back-seat passenger thrown to her death on an expressway was jailed for eight months and banned from the road for five years yesterday.

Muhammad Khairullah Abdul Latif, 25, pleaded guilty to causing death by a rash act and failing to ensure the victim was wearing a seat belt, for which he was fined $600.

Deputy Public Prosecutor Tan Si En told the court that Khairullah had met his two friends, Madam Ratu Wahedah Banakhani Hamzah Khan, 41, and Mr Supri Sapari, 45, at a coffee shop in Clementi around midnight on Aug 2 last year.

The trio then proceeded to a pub at Beauty World Centre where they shared six cans of beer before heading to another pub in Orchard Road, which they left at about 2.30am.

Mr Supri got into the Toyota's front passenger seat, fastened his seat belt and fell asleep while Madam Khan got in the back.

Khairullah was driving at up to 110kmh along the Ayer Rajah Expressway (AYE) shortly before 4am when he saw a puddle and filtered right without checking his rear- view mirror .

He encroached into the path of a car and while midway through the centre lane, he suddenly saw another car behind very near him.

In a panicked state, he accelerated and swerved, causing his car to spin and hit a guard rail in the centre. It skidded left before stopping - flinging Madam Khan out of the rear windscreen into a small drain.

A paramedic pronounced her dead at 4.45am.

Khairullah failed an initial breathalyser test but passed a second at the Traffic Police Department.

He could have been jailed for up to five years and/or fined for causing death by a rash act.

A third charge of causing hurt to Mr Supri, the front-seat passenger, through a rash act was taken into consideration.

The maximum punishment for the seat-belt offence is a $1,000 fine or three months' jail.