The regulations concerning signs and road markings state that all double lines are*Combined lines.

This particular combo is called a Double prohibitory line. You may not cross over, drive on or to the left of a yellow prohibitory line.

The double prohibitory line is used as a centre line if circumstances make it necessary to prohibit overtaking or any crossing of the centre line for both road users in both directions. Double yellow prohibitory lines are typically used on three-lane roads with traffic in both directions.

Here are some other examples of line combinations: