Cargo Securement and Weight Distribution
What this domain tests
This domain tests cargo securement and weight distribution for combination vehicles: tiedown requirements, working load limits, axle and gross weight limits, and load placement. The exam expects you to know that legal weight is not the same as safe weight distribution.
Core rules
- Cargo must be secured against shifting, sliding, rolling and falling. Use tiedowns, chains, straps, binders, blocking or headboards as appropriate.
- The aggregate working load limit of all tiedowns must be at least 50% of the cargo weight. Working load limit is not the same as breaking strength; do not use a strap's breaking strength as its capacity.
- Tiedown count depends on article length: one tiedown for articles 5 feet or less, two for articles 5 to 10 feet, and one additional tiedown for each additional 10 feet.
- Do not exceed axle, tire, bridge-formula or gross vehicle weight ratings. Distribute weight so the steer axle has enough load for steering, drive axles are not overloaded and the trailer axles are within limits.
- Keep the center of gravity low and centered. High or rearward loads reduce steering and brake balance and increase rollover risk.
- Recheck securement after the first few miles and at stops. Straps can stretch, binders can loosen and loads can settle.
Worked example
A 40,000-pound load needs an aggregate tiedown working load limit of at least 20,000 pounds. Four straps rated at 5,000 pounds WLL each give exactly 20,000 pounds, meeting the minimum. If the load is 12 feet long, however, the length rule requires at least three tiedowns, so four is acceptable only if their placement and angles secure the load. If the driver uses straps rated by 10,000-pound breaking strength, the WLL may be only 3,333 pounds each, so four straps would not meet the requirement.
Traps
Confusing breaking strength with working load limit, counting tiedowns without checking placement, overloading trailer axles while underloading the steer axle, and failing to recheck the load are common errors. Also remember that a tarp is not a tiedown.