Loads That Shift Weight
Maintaining the control of a truck is difficult when weight slips especially on poor road conditions. Livestock shifts weight when turning corners or when making sudden swerves. Liquids in tanks will slosh back and forth when baffles are not installed in the tank.
On September 27, 2002, the Federal Motor Carrier Safety Administration (FMCSA) published new cargo securement rules. Motor carriers operating in interstate commerce must comply with the new requirements beginning January 1, 2004. The new rules require motor carriers to change the way they use cargo securement devices to prevent articles from shifting on or within, or falling from commercial motor vehicles. The changes may require motor carriers to increase the number of tie-downs used to secure certain types of cargo. The intent of the new requirements is to reduce the number of accidents caused by cargo shifting on or within, or falling from, commercial motor vehicles operating in interstate commerce, and to harmonize to the greatest extent practicable U.S., Canadian, and Mexican cargo securement regulations.
FMCSA has adopted new performance requirements for cargo securement systems. They must withstand those performance criterions concerning deceleration in the forward direction, and acceleration in the rearward and lateral directions. Deceleration is the rate at which the speed of the vehicle decreases when the brakes are applied, and acceleration is the rate at which the speed of the vehicle increases in the lateral direction or sideways (while the vehicle is turning), or in the rearward direction (when the vehicle is being driven in reverse and makes contact with a loading dock). Acceleration and deceleration values are commonly reported as a proportion of the acceleration due to the force of gravity (g). FMCSA requires that cargo securement systems be capable of withstanding the forces associated with following three deceleration/accelerations, applied separately:
- 0.8 g deceleration in the forward direction;
- 0.5 g acceleration in the rearward direction; and
- 0.5 g acceleration in a lateral direction.
Cargo must be firmly immobilized or secured on or within a vehicle by structures of adequate strength, dunnage (loose materials used to support and protect cargo) or dunnage bags (inflatable bags intended to fill space between articles of cargo or between cargo and the wall of the vehicle), shoring bars, tie-downs or a combination of these. Articles of cargo that are likely to roll must be restrained by chocks, wedges, a cradle or other equivalent means to prevent rolling. The means of preventing rolling must not be capable of becoming unintentionally unfastened or loose while the vehicle is in transit. Articles of cargo placed beside each other and secured by transverse tie-downs must be:
- Placed in direct contact with each other, or
- Prevented from shifting towards each other while in transit.