The physics of loading a truck
Securing cargo onto a truck is very much a question of common sense. Understanding the basic physics of the situation can help avoid accidents down the road.
Cargo that is inadequately secured on a truck can potentially be life threatening for the driver, pedestrians as well as drivers of other vehicles.
The basic physical principle is that when a vehicle brakes, the load will strive to continue in its original direction independently of the vehicle, unless of course it is properly lashed down.
“Securing cargo on a truck is about taking into account four very important parameters – the friction between the cargo and the truck bed, the cargo’s dimensions, its weight and center of gravity,” says Peter Andersson, President of Mariterm, a Swedish company that conducts cargo securing courses for the trucking and maritime industries. “Cargo should never tip or slide. That is when accidents happen.”
Road safety measures
According to Andersson, the most dangerous instances for a truck loaded with cargo occur during hard and sudden braking, strong acceleration, hard cornering on roundabouts and rapidly changing lanes. Without appropriate restraints, these are the moments when the physical forces on the cargo are the strongest and potentially most catastrophic.
“Many say that the best advice is to drive calmly, which is true. At the same time, you never know when something unforeseen is going to happen,” says Andersson.
According to international rules, cargo restraints in the forms of chains and blocks should be able to withstand 0.8 times the weight of the cargo during heavy braking, and 0.5 times the weight during a turn.
But according to the EU’s Cargo Securing for Road Transport European Best Practice Guidelines, which publishes tables relating weight to how many restraints are needed, friction tables and so on, the principles of cargo securing should be regarded as the minimum requirements.
“During heavy braking, the force exerted by the cargo can be very high and nearly equal to the weight of the cargo. Greater forces may be encountered if the vehicle, for example, is involved in an accident,” says the report.
Driver responsibilities
Besides center of gravity, friction, and weight, some other things to consider when loading a truck include the rigidity of the cargo, the load distribution, and the choice of an appropriate vehicle.
Another important point when securing cargo on a truck is that maybe it will continue its journey on a train or on a ship, both of which pose different force scenarios on the cargo than road transport.
“In our training, we urge people to think one step ahead and do it right from the beginning,” says Andersson.
So who is ultimately responsible?
“That is a complicated question and it differs from country to country,” says Andersson. “Many drivers often go to pick-up a pre-loaded trailer and expect it to be fine. In Sweden, the driver is ultimately responsible whereas in Germany it is the driver, the sender, and the trucking company that share responsibility. But ultimately the driver should always make sure that his rig is secured correctly.”
Scenarios
When starting from a standstill, the cargo load acts with a force that corresponds to half the cargo’s weight when directed towards the rear of the vehicle.
When turning corners, the sidewise force may reach half the weight of the cargo. In the case of unstable loads, you also need to account for an additional roll factor.
When braking, the force directed towards the front may equal 80 percent of the cargo’s weight. In this case, the cargo is stowed up against the headboard.
Friction alone cannot prevent cargo from sliding. Securing the cargo to the platform and base blocking with chains or other lashings can stop the cargo from sliding sidewise. Beams and profiles should be stowed on wedge beds and secured with loop lashings.
Driver Checklist for Cargo Securing
The ten most important tips for cargo securing according to the EU’s Cargo Securing for Road Transport European Best Practice Guidelines:
Check that load platform, bodywork, and load securing equipment are sound and serviceable.
Secure cargo so that it cannot move, roll over, wander because of vibrations, fall off the vehicle or tip.
Determine the securing method(s) best adapted to the cargo (locking, blocking, lashing, top-over lashing, or a combination of these).
Check that the vehicle and blocking equipment manufacturer’s recommendations are adhered to.
The securing equipment must withstand the conditions of the journey like bad road and weather conditions.
Ensure that the cargo is distributed in such a way that the center of gravity of the total cargo lies as close as possible to the longitudinal axis of the truck and is kept as low as possible.
Check the cargo securing regularly, especially after heavy braking.
Use friction mats, boards, straps and beams to support the cargo.
Ensure that the securing equipment does not damage the cargo.
Drive smoothly and avoid brisk change of direction and heavy braking.
