Western Australian Consolidated Regulations Western Australian Consolidated Regulations (1) On a semi-trailer
or a dog trailer —
(a) the
distance between the point of articulation at the front of the trailer and the
rear overhang line must not be over 9.5 m; and
(b) the
distance between the point of articulation at the front of the trailer and the
rear of the trailer must not be over 12.3 m.
(2) A projection
forward of the point of articulation at the front of a semi-trailer must be
contained within a radius of 1.9 m from the point of articulation. 
Dimension limits for a semi-trailer
(3) If a semi-trailer
has 2 or more points of articulation at the front of the trailer, it must
comply with subrules (1) and (2) when measured at one of the points.
(4) A trailer built to
carry cattle, sheep, pigs or horses on 2 or more partly or completely
overlapping decks must not have over 12.5 m of its length available for
the carriage of animals.
(5) For
subrule (4), the length available for the carriage of animals on a
trailer is measured from the inside of the front wall or door of the trailer
to the inside of the rear wall or door of the trailer, with any intervening
partitions disregarded.