Distribute the Load to Avoid Over-Weight Axles and The California Bridge Formula Problem

Because loading a truck is often based on tribal knowledge, many companies suffer from:

  • Reloading the vehicle requires changing how the load is distributed to eliminate violating legal limits on an axle or group of axles. Carrier and additional labor costs mount up, but the biggest issues include the need to reshuffle dock schedules and customers not getting the product when they want it.
  • In-transit damage caused by the load toppling or shifting

To mitigate these problems, many companies reduce the load size to provide a greater safety margin for loader error, i.e., reduce the payload. This is a vast but hidden cost, as transportation represents 70% of supply chain costs in most consumer products companies, and reductions can be in excess of 10%. 

Tribal knowledge is not limited to how the product should be distributed in the load. Even experienced transportation managers often don’t understand the regulations in each state or, for that matter, federally.

Consider this example from a Fortune 100 consumer products company that suffered from loads failing at the weigh scale in California. The company was often forced to pay charges ranging from fines to unloading fees and product loss. All this was because the loaders didn’t know how to distribute the load. In reaction, they reduced the payload of these shipments by more than 10%. We’ll examine this company’s predicament in more depth later. 

Understanding the goals

While the first goal is to be legal, the next goal is to ship the product and have it arrive damage-free and at the best possible cost.  Cost-effectiveness requires that no truck capacity is wasted.  The laws in each state are different, with California always being singled out as the most restrictive. Before we go into what these rules are, here are some definitions that are the minimum on Federal highways:

  • Gross Vehicle Weight (GVW): The maximum GVW for trucks on the Interstate Highway System is 80,000 pounds
  • Single Axle Weight: The maximum weight allowed on a single axle is 20,000 pounds
  • Tandem Axle Weight: The maximum weight for tandem axles (two axles spaced close together) is 34,000 pound
  • Bridge Formula: The Bridge Gross Weight Formula determines the maximum allowable weight on groups of axles based on the distance between them. This formula helps prevent excessive stress on bridges.

Fortunately, the Bridge Formula and gross weight for the 5-axle combination (the standard US tractor trailer) are almost uniformly applied nationwide, at 80,000 pounds.

State Variations

While some intrastate regulations or permit-legal situations allow more gross or axle weight or, in some cases, on “smaller roads” away from the federal highway system, the gross limit may be lower.  Consider Illinois that, for the most part, allows  a full gross weight of 80,000#

But even then, it gets more interesting: Illinois’s maximum truck weight of 73,280 pounds applies to certain non-designated highways. These are typically local roads not part of the state or federal highway system.

The most significant variation from state to state is axle placement.

While many states allow trailer tandem axles to be placed in any of the many “pins” in the trailer, they restrict the maximum rearward position of the tandem.  Consider California where the restriction is often misnamed the “California Bridge Formula. ” The rear-most axle can be no more than 40 feet from the trailer kingpin. Therefore, the rule should be more accurately called the axle placement or kingpin law.

Other states have similar laws –but not as stringent, for example Illinois:

While some states have no such restrictions.

How loads should be distributed is impacted by axle placement.

Just as a seesaw provides different “lifts” based on the weight distribution, a trailer functions similarly. The positioning of the rear axle group determines the axle weight exerted for a given load.

Consider a pallet placed at the 48ft mark in a trailer.  If the axles are at the rear, there is little weight transfer to the front of the trailer.  On the other hand, if the trailer is in the California setting, there is a weight lifted off the kingpin:

Axles at the back of the trailer -little weight added to the kingpin

Axles at the California setting –white taken off the kingpin                    

Case study – Load Distribution When Shipping to California

A Fortune 100 consumer products company faced issues with loads being stopped in California because loaders lacked knowledge about proper load distribution. The loaders may not have known the rules—but more likely, they knew them but had difficulty putting them into practice.  Why? Because the physics of moments, which is the mathematics behind determining the axle weights, is complex and requires many calculations that are way too hard to do without the aid of a computer.

This company took the route many companies choose – they dropped the target load weight at a substantial cost to the overall transportation costs.  Fortunately, they soon recognized the unsustainable nature of this cost and sought a solution.  They found AutoO2 from ProvisionAi.  AutoO2 calculates the best way to distribute the load.   Here is an example of an intermodal load going to California:

Reading the loading diagram:

  • Each box represents a floor position
  • The letter “T” indicates the pallet is turned (i.e., loaded on the 48” dimension)
  • The numbers in the box:
    • Two lines indicate that the product is stacked
    • The numbers in the box – Product ID  (Weight of the product and pallet, weight that can be stacked on top, the height of the pallet)
  • A/B indicated airbag (Dunnage)

The AutoO2 software allowed three more pallets and thousands of more pounds to be added while maintaining axle legality.

Determining the best way to distribute the load.

Loading a trailer is a complex combinatorial problem that is complicated by:

  • Ensuring items are stacked so there is no in-transit crushing
  • Ensure the load won’t shift when a truck brakes or corners rapidly.
  • Creating a plan that has dunnage placed appropriately.

Of course, many of the ways to distribute the load are state-specific, being dependent on the axle positioning. Additionally, each site may have its particular loading method. For example, if the load stores all products on 40 x 48 pallets on the 40-inch side, it would prefer to load without turning each pallet. Also, some locations may not use the standard airbag but special tapes or load stability bars, which will require an additional understanding of how unit loads should be positioned.   

What about the trucks themselves?

Many argue that since every truck can vary, adding a safety margin is essential. This is true, but the key caveat is to aim for reasonable limits rather than the absolute minimum. For example, consider over 100 empty refrigerated trucks. Their capacity is calculated by subtracting the tare weight from 80,000 pounds. 

Should the heaviest truck, with a capacity under 40,000 pounds, set the standard for all vehicles? Of course not. Management must determine the cut-off using accurate data, not tribal knowledge. In this case, 76% of trucks can legally carry 44,500 pounds. AutoO2 optimizes load placement to approach that goal. While hitting the exact target may be rare, incremental stack weights can reduce the total load slightly.

Summary: Distribute the Load to Avoid Over-Weight Axles and The California Bridge Formula Problem

Using AutoO2 technology to “optimally” distribute the load generates significant transportation savings, improves customer service, and eliminates the “reload” disruption in shipping operations. AutoO2 manages disruption and enhances profitability, especially for shipments going to California.