O'Grady v Sparling[1] was a landmark Supreme Court of Canada decision, on the constitutionality of overlapping federal and provincial laws.

Judson held that "the power of a provincial legislature to enact legislation for the regulation of highway traffic is undoubted".

Thus the two governments can make law on the same matter by creating a distinction between the types of culpability:[3] There is a fundamental difference between the subject-matter of these two pieces of legislation which the appellant's argument does not recognize.

He stated that the leading case on the matter, Provincial Secretary of Prince Edward Island v. Egan, cannot be read so broadly as to give the provinces unlimited powers over highways.

Matters in relation to those within the federal government's powers are exclusive and comprehensive and do not allow for complementary law: In my opinion when Parliament has expressed in an Act its decision that a certain kind or degree of negligence in the operation of a motor vehicle shall be punishable as a crime against the state it follows that it has decided that no less culpable kind or degree of negligence in such operation shall be so punishable.