The Department of Transport (DoT), in conjunction with Main Roads WA, has allowed the
conditional licensing (registration) and use of 14.63m long semi-trailers in this state for a
number of years. Recently, national dimensional limits for semi-trailer length have
changed and this updated document reflects these changes.
Compliance with nationally accepted dimensions
The following dimensional limits have not changed and apply irrespective of the trailer
length:
• Maximum overall length of the prime mover and semi-trailer combination of 19m
• Maximum width of 2.5m
• Maximum S Dimension of 9.5m (where “S Dimension” is the distance between the
centreline of the king pin and the centreline of the rear axle group of the semi-trailer)
• Forward projection of the semi-trailer must be contained within a radius of 1.9m
• Maximum rear overhang of 3.7m of 60% or the “S Dimension”, whichever is the
lesser
