A recent appeal decision in the Supreme Court of Western Australia provides a clear example of how the scope of a motorist's duty to warn other road users about hazards depends greatly on the particular circumstances of the case. These circumstances will often include speeds and distances of travel, driver reaction times and visibility.

Ms Pearce crashed her car into a cow, then swerved and came to a stop in the opposite lane. She was not negligent in hitting the cow. She sat in shock for a couple of seconds then got out of her car, believing that the windscreen had made a cracking noise and might collapse into the car.

Mr Burns was driving along 13 seconds behind Ms Pearce. He also collided with the cow, and sustained injuries. Mr Burns alleged that Ms Pearce was negligent for failing to turn on her hazard lights as a warning to him.

The scope of a motorist's duty to warn is what, if anything, a reasonable person would have done in response to the foreseeable risks to other road users. Given her initial shock and her fear that the windscreen might break, the trial judge held that Ms Pearce had not breached her duty of care to Mr Burns when she got out of her car without first turning on her hazard lights.

The activation of the hazard lights would have only occurred about five seconds before Mr Burns collided with the cow. It would not have made any significant difference to the action Mr Burns took. He only started braking when he saw the cow on the road in front of him – not when he saw Ms Pearce's brake lights go on just before she hit the cow, or when he saw Ms Pearce's car swerve into the opposite lane. He had ample warning that something was amiss and he should have used that time to slow down and avoid hitting the cow.

Mr Burns' claim was dismissed and the trial judge's findings were upheld on appeal.

This case can be contrasted to the leading Queensland case Lawes v. Nominal Defendant, where a driver who struck and killed a horse then left the scene was held responsible for the injuries of a motorcyclist who later struck the same horse. The interval between the two accidents would have been long enough for the driver to have effectively warned other road users of the danger by illuminating the horse with headlights and turning on the vehicle's hazard lights.

In both cases, the critical deciding factors were the interval between the first and second accidents, and the probability of the second accident being avoidable if early warning signals had been given.

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