What is load planning?

Deciding how cargo is placed in a truck, trailer or container — what fits, in what order, and how the weight is spread — so the load is legal, secure and uses the space well.

What is the bridge formula?

The US rule that limits the weight on any group of axles by how many axles it has and how far apart they are: W = 500 × (LN ÷ (N − 1) + 12N + 36), in pounds and feet.

Why is load planning hard to automate?

Packing boxes into a container is a strongly NP-hard problem, so exact answers are impractical at scale; software uses heuristics and adds rules for weight, fragility and delivery order.

Term

Load planning

Load planning is deciding how cargo goes into a truck, trailer or container — what fits, in what order, and where the weight sits — so the load is legal, stable and uses the space. It has to respect gross and axle weight limits, keep the centre of gravity in the right place, and match the order of delivery stops.

Also called load plan, truck load planning, container load planning, axle weight distributionUpdated 12 October 2026

The limits a plan must meet

Limit	United States (Interstate)	European Union
Single axle	20,000 lb (9.07 t)	10 t non-driving; 11.5 t driving
Tandem axle	34,000 lb (15.42 t)	Depends on axle spacing
Gross vehicle weight	80,000 lb (36.29 t)	40 t for 5–6 axles; 44 t with containers up to 45 ft in intermodal transport

A truck can be under its gross limit and still be illegal if one axle group carries too much. That is why where the weight sits matters as much as how much there is.

Worked example: the US bridge formula

US rules cap the weight on any group of axles with W = 500 × (LN ÷ (N − 1) + 12N + 36), where W is the weight in pounds, L the distance in feet between the outer axles of the group, and N the number of axles in it.

Tandem, L = 4 ft, N = 2: 500 × (8 + 24 + 36) = 34,000 lb · Whole truck, L = 51 ft, N = 5: 500 × (63.75 + 60 + 36) = 79,875 → 80,000 lb

A five-axle truck needs about 51 ft between its first and last axles to carry the full 80,000 lb — shorter, and the formula lowers its legal weight.

Why it is hard

Fitting boxes into containers is, mathematically, a strongly NP-hard problem — Martello, Pisinger and Vigo describe the three-dimensional version as extremely difficult to solve in practice — so software uses heuristics, and planners add the rules maths alone misses: heavy first, fragile on top, last stop nearest the door.

The IMO, ILO and UNECE Code of Practice for Packing of Cargo Transport Units — the CTU Code, non-mandatory — sets out the safety side. It warns that containers on semi-trailers often have their centre of gravity forward of centre, overloading the truck's front axles, and that a misdeclared gross mass can overload the road vehicle. In the EU, roadside inspectors check lashing against standards including EN 12195-1.

The mistake people make

Planning by volume and weight totals only. A load that fits and weighs under the limit can still overload an axle, shift in braking, or bury the first drop behind the last.

FAQ

Load planning: common questions

What is load planning?: Deciding how cargo is placed in a truck, trailer or container — what fits, in what order, and how the weight is spread — so the load is legal, secure and uses the space well.
What is the bridge formula?: The US rule that limits the weight on any group of axles by how many axles it has and how far apart they are: W = 500 × (LN ÷ (N − 1) + 12N + 36), in pounds and feet.
Why is load planning hard to automate?: Packing boxes into a container is a strongly NP-hard problem, so exact answers are impractical at scale; software uses heuristics and adds rules for weight, fragility and delivery order.

Sources

On Traqo: Truck Utilisation Calculator shows how much payload and volume a load uses.