A motorist was killed on the Queen Elizabeth Way near Oakville on Thursday night when a tire came off a tractor-trailer and hit her car.

The 41-year-old Oakville woman was driving a Mercedes westbound around 9 p.m. when a set of rear dual tires came loose from the tractor-trailer in the eastbound lane and bounced over the median.

Her car careened into the ditch after one of the tires hit it.

The woman was pronounced dead at the scene. Her name has not been released pending notification of next of kin.

The other tire struck a tractor-trailer, causing it to lose part of its load. The driver was not injured.

Ontario Provincial Police stopped the tractor-trailer that lost its tires further down the highway and is now holding the vehicle for inspection.

Police said charges are likely.

Number of 'wheel separations' falls

The OPP said that while incidents such as flying tires, also known as wheel separations, were quite common in previous decades, the number has dropped in recent years because of tough legislation.

"We found that a lot of the companies and the maintenance of those vehicles were upscaled," said OPP Const. David Woodford.

Coroner's inquests called into two separate truck tire fatalities sparked new regulations in Ontario in 1997.

Among other things, the Comprehensive Road Safety Act set fines for truck owners from $2,000 to $50,000 for wheel separations. The fines apply to truck owners or operators, not the drivers.

Since then, flying tire incidents have decreased by 58 per cent — from 215 in 1997 to 90 in 2005.