I have been asked by a Fleet Manager to remind their drivers how to work out the weight loadings for a bus.
Here's an outline of the terms used, the way to estimate load weights, and ensure your bus or coach can handle them.
Work Out Your Bus Specifications:You need to know your various definitions for vehicle weights:
Tare Mass or Weight
This is the weight of an empty standard vehicle with all of its fluids (oils, coolants) but with only 10 litres of fuel in the tank. There are no passengers, luggage or freight.
Kerb Mass or Weight
This is the same as Tare Mass, but with a full tank of fuel and without any accessories fitted (bull bars, tow bars, etc).
Gross Vehicle Mass (GVM) or Weight (GVW)
This is the maximum your bus or coach can weigh when fully loaded as specified by the manufacturer. You will usually find this GVM figure on the vehicle's weight placard (generally found in the driver's door opening) or in the owner's manual. So GVM is the Kerb Mass plus driver, passengers, luggage, freight, tools and whatever else you're taking with you.
And if you're towing a trailer, GVM also includes the Tow Ball Download.
Gross Vehicle Axle Mass or Weight
This is the maximum load that your vehicle's front and rear axles can carry as specified by the manufacturer. The combined gross axle weights usually exceed the GVM, to provide a safety margin. Even so, it's important to know that your vehicle's GVM has been distributed evenly for safe and efficient operation.
If you are towing a trailer:
Tow Bar Download (TBD)
A tow bar will have a placard or similar showing the maximum tow bar capacity and maximum tow bar download (maximum amount of trailer weight that can push down on the tow bar).
Aggregate Trailer Mass (ATM) or Weight (ATW)
This is the Gross Trailer Mass (GTM) plus the Tow Bar Download. In other words, the ATM is the maximum towing weight of the trailer as specified by the manufacturer.
Gross Combination Mass (GCM) or Weight (GCW)
This is the maximum weight allowed for your vehicle and trailer combined, as specified by the tow vehicle's manufacturer. This is where you have to pay close attention to your vehicle's GVM and your trailer's ATM, because those two figures determine the GCM and one directly affects the other.
These are all summarised in the following diagram:
Where Do I Find These Values for My Bus?The best places to find out the specifications for your vehicle is:
- Registration Certificates or Labels
- Insurance Certificates
- Vehicle Placards and Modification Plates
- Vehicle Instruction Manual
- Dealers Technical Specification data
If you are really keen, you can go to a public weighbridge with the bus or coach, and get the unladen weight with all your standard equipment (that you normally carry). This can provide you with a base weight to work from.
How Do I Workout if I am Loaded Correctly?The first step is calculate your load, remembering to include:
- driver and passenger weights
Driver / Passenger Weights
I recommend working on the aviation industry specifications (see CASA link in references).
They estimate passenger weights based on age and gender as follows:
You should note, this data is nearly 30 years old,
so I would recommend adding 10kg to these figures!
So the passenger weights would be a multiple of the number of each type of passenger by the average weight (from the table).
eg. You will be carrying 20 adults (including yourself), 6 teenagers and 10 children.
20 adults x [assume males to be safe] 96kg = 1920kg
6 teenagers x [assume males to be safe] 75kg = 450kg
10 children x 44kg = 440kg
TOTAL = 2810kg
LuggageIt is impractical to measure luggage weights, under most situations, but you can estimate:
School bags (primary) = 5kg
School bags (secondary) = 8kg
Overnight bags = 10kg
Extended luggage = 20+kg
Eg. In the above example, the adults carry overnight bags, the children and teenagers carry school bags.
20 adults x 10kg = 200kg
6 teenagers x 8kg = 48kg
10 children x 5kg = 50kg
TOTAL = 298kg
FreightFreight is usually labelled with mass and dimension data. Otherwise, you can estimate by pushing against heavy items to estimate their weight.
How do I Calculate All This Weight?Firstly, work out what your maximum payload (passengers, luggage and freight):
Payload (max) = GVM - Kerb*
eg. if GVM = 10t and Kerb* = 6.45t then Payload = 3.55t max.
* Kerb is here used to mean empty but with your equipment loaded.
Next, estimate the payload weight:
Payload (est) = passenger wt + luggage wt + freight wt
eg. for the above example, with no freight:
Payload (est) = 2810kg + 298kg = 3108kg
Compare the Payload (max) with the Payload (est):
eg. P[max] = 3.55t and P[est] = 3.11t therefore LEGAL.
Finally, consider the configuration of your bus or coach (ie. number of axles, positions of axles and individual axle loadings) to ensure the weight (ie. passengers, luggage and freight) is evenly distributed to maintain LEGAL and SAFE loading.
More information on this can be found in the Australian Bus and Coach Drivers' Guide.
ReferencesCIVIL AVIATION SAFETY AUTHORITY (1990) STANDARD PASSENGER AND BAGGAGE WEIGHTS
Duffy, J (2013) Australian Bus and Coach Drivers' Guide