The Roads and Traffic Authority of New South Wales v O'Reilly & Ors

The Roads and Traffic Authority of New South Wales (RTA) appealed against a Local Court decision in which three defendants were acquitted of speeding offences. The defendants were charged with exceeding the speed limit in a 60 km/h zone, but each claimed they genuinely believed the speed limit was 80 km/h due to the absence of speed limit signs. The defendants were found not guilty by the Local Court, which ruled that their mistake about the speed limit was a factual error. The RTA argued that the mistake was of law, which would render it irrelevant to their defence.

The appeal before the Court of Appeal required determining whether the defendants' belief about the speed limit constituted a mistake of fact or a mistake of law. If the former, the mistake would be relevant to the defence of mistaken belief. However, if the latter, the mistake would be irrelevant, as a mistaken belief about the law is not a defence. The court considered whether the defendants' belief about the speed limit was based on an honest and reasonable misunderstanding of the traffic signs or whether it was a failure to understand the law correctly.

The Court of Appeal held that the defendants' belief was a mistake of law, as it arose from a failure to understand the legal framework governing speed limits rather than an honest misunderstanding of the traffic signs. The court emphasised that the correct speed limit is a matter of law, and a mistaken belief about it does not constitute a valid defence. Consequently, the appeals were upheld, and the orders made by the Local Court were set aside. The defendants' convictions for speeding were reinstated, and the RTA was awarded costs.