3.1 Understanding Your Vehicle

When deciding on which vehicle you should use to carry a given load you need to consider several factors including:

  • Is body type appropriate for the load?
  • The technical capacity of the vehicle to carry the load. (mass and dimensions)
  • Whether the load and vehicle combination are restricted in which routes they are allowed to travel on (the technical term for this is whether the vehicle (plus load) has suitable access.
  • The safety of the combination.

In relation to choosing an appropriate body type the following table describes common body types and their typical uses. Unusual loads my require body types customised for the particular load.

TankerTankers are vehicles where the product in
completely enclosed (blocked) by the vehicle and
are typically used for liquids and fine powdery dry
bulk products.
Tippers (various types)Tippers are vehicles where the load is blocked in
the horizontal directions and can be loaded into the
top of the vehicle using a conveyor belt or
machinery. Tippers can be unloaded by tilting the
body to discharge the load. Tippers may use a net
or tarpaulin to constrain vertical movement of the
Pantech or Van bodiesA Pantech or van body is a body with rigid sides
which constrains the movement of the load in all
directions. However, the load may need to be
constrained within the body to ensure that the load
does not move and either damage the load or make
the vehicle unstable. These vehicles are often used
for general freight which may be boxed, palletised
or otherwise unitised. The body of the vehicle will
typically have anchorages on the inside of the
vehicle to facilitate attachment of load restraint
devices. In these vehicle the freight must be loaded
and unloaded through the rear doors.
CurtainsiderCurtainsider vehicles are bodies used to transport
general freight which have flexible sides which can
be pulled aside to facilitate loading the vehicle from
the side. These vehicles are often used when there
are multiple loads which will be picked up or
dropped off in different places.
Fridge/freezerFridge or freezer vehicles are Van bodies which
have refrigeration or freezer units and insulation
added to allow the transport of temperature
sensitive loads.
Flat top or tray bodiesThese are vehicles with a flat rigid tray where a load
can be placed on the tray and restrained by either
tie down or direct restraint. These bodies often
have a headboard and typically have load
anchorage points around the sides of the tray.
Drop DeckA drop deck trailer is a semi trailer where the load
surface of the tray steps down to below the height
of the fifth wheel coupling. This allows the centre of
gravity to be lowered increasing stability and will
also lower the overall height of the load possibly
allowing it to pass under low structures such as
bridges. It also typically provides a vertical surface
where the deck height changes which can be used
for blocking of the forces pushing forward on the
Deck widenerDeck wideners are designed to allow wide loads to
be carried without any of the load overhanging the
sides of the vehicle’s deck. They are often
combined with drop deck or low loader designs.
Tilt trayTilt tray bodies are bodies where the tray on the
vehicle can be tilted to allow loads to be pulled up
onto the tray typically with an electric winch.
Low LoaderA low loader is a trailer designed to have a low deck
and low sides to allow long and or wide loads to be
carried. In contrast to a drop deck trailer a low
loader usually uses a dolly to manage the
connection to the fifth wheel and allow the full
trailer deck to be at the same height. These trailers
are often used top carry large pieces of machinery
or equipment.
Skel trailersA skel (or skeleton) trailer is a trailer with a minimal
deck structure that is designed to carry standard
ISO container using twist lock connectors.
Specialty bodies – eg logging, steel, glass sheetsTrailers may have specially designed bodies to
facilitate the carrying of a particular type of load.
Trailers designed to haul timber are an obvious
example of these trailers.

The technical capability of the vehicle or combination to carry the load will be determined by a range of factors including:

  • The vehicle manufacturers rating of the permitted Gross vehicle Mass (GVM) and the Gross Combination Mass (GCM) in the case of articulated vehicles)
  • The dimensions of the vehicle and load combined (where possible you should have the load sit within the dimensions of the vehicle and you should ensure the vehicle does not exceed permitted heights.

In relation to the routes vehicles are permitted to travel on road managers may restrict the mass or dimensions of vehicles. Because not all roads and bridges are built to the same standard, road managers control which vehicles can use which roads. The standard axle mass and dimension limits that allow access to most of the road network (unless prohibited by signage) are called General Mass Limits or GML. The NHVR has a useful guide to the mass and dimension limits for particular common vehicle types which is available here General mass and dimension limits | NHVR. Vehicles which do not meet the requirements for general access are termed restricted access vehicles and may be permitted to use portions of the road system under access permits or notices, which may place conditions on the vehicle or operator to control the movement of the vehicle.

In relation to safety key aspects will be the stability of the vehicle and its ability to steer and brake properly.

Common problems with stability occur when the centre of gravity of the vehicle plus the load is high.
Where stability is an issue it may be better to choose a different vehicle types such as a drop deck, a low loader (to lower the centre of gravity or a widening trailer.

Click on this animation to see how swithcing to a low loader can improve stability

Positioning the load correctly on the vehicle may impact on stability and may also interfere with a vehicles ability to steer or brake properly are related to the positioning of the load and the balance of the axle masses between the axles. Where a load is unbalanced side to side it may increase the likelihood of the vehicle rolling.

And where a load in unbalanced longitudinally it may impact on the braking or steering of the vehicle.

Another issue which can impact on stability is shifting loads. This is particularly important for loose bulk loads which need to be adequately contained and liquids where containers carrying liquids may need baffles to control the movement of the load.


In order for a vehicles able to carry a load you need to ensure:

  • A suitable body type has been chosen for the load.
  • The total Mass for the vehicle or combination (tare plus fuel, plus passengers plus load) must no more than the GVM for the vehicle and less than GCM of the Prime Mover or Truck (in the case of a rigid truck towing trailers) for a heavy vehicle combination.
  • If the vehicle does not meet the mass and dimension limits for general access, access permissions for the laden vehicle combination need to be in place (either by a notice or a permit).
  • The mass of the vehicle in total and the axle loads on every axle on the combination need to be within the mass limits for the vehicle or combination on the required routes.
  • The load needs to be suitably positioned on the vehicle to maintain stability, steering and braking.
  • The operator and driver need to be aware of any conditions related to any notices or permits.
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