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Would you stake your life, right now, on the condition of your equipment?
NEWS | June 6, 2022

Ground Vehicles: Don’t go off the Rails with Secondary Cargo Loads

On Pages 11-15 of PS 758 (Jan 16), we told you that when equipment, palletized cargo or small vehicles are loaded onto or into the cargo areas of trucks or trailers transported by rail, it’s called a secondary cargo load.
There’s little official guidance in the Association of American Railroads (AAR) Open Top Loading Rules (OTLR) Manual (Aug 20) that covers these loads.
There’s also very limited guidance in the TEA Modal Instruction (MI) 19 Tiedown Instructions for Rail Movements (Aug 21) specifically covering secondary loads. That’s why properly restraining a secondary load is difficult and requires prior planning. It’s important that planners use caution and are sure that rail carriers approve secondary loads, prior to finalizing a rail loading plan.
Secondary loads that involve wheeled or tracked vehicles are NOT automatically approved. How are they approved? The load must successfully complete rail impact testing. Once the test is successfully completed, the vehicle will be assigned a loading figure in the AAR’s OTLR manual. The loading figure is a graphic display with the info that’s required to properly load and secure that specific secondary load, necessary equipment and any additional requirements. Here’s an example of a loading figure:
Loading Fig 88H for M1000 HET
Loading Fig 88H for M1000 HET
Considerations for Planning Secondary Cargo Loads for Rail Transport

Planning is the key to success. When it comes to the movement of secondary loads consisting of general cargo, you’ll need to answer these five (5) questions: 
  • Has the primary vehicle or trailer been tested and approved to carry a payload (secondary cargo) for rail transport?
  • Does the secondary general cargo load fall within the approved payload capacity of the cargo vehicle or trailer?
  • Can the secondary general cargo load be adequately secured to the primary vehicle or trailer that meets the restraint requirement for rail transport?
  • Does the primary vehicle or trailer with a general cargo load fit within the required rail clearance envelopes?
  • Is the cargo properly packaged, palletized and/or crated?
You can find approved weights of general cargo for specific vehicles, trailers and equipment as secondary loads in Table 1 of the AAR OTLR, shown below. The listed vehicles, trailers and equipment have been approved by successful rail impact testing and their maximum payload weight, if applicable is also shown.
Table 1 of the AAR OTL (PLS=Palletized Load System)
Vehicle, Trailer or Equipment Approved General Cargo Secondary Load Weight
M870A1 trailer No secondary payload
M870A3 trailer 24,950 lbs
M871A3 trailer 45,000 lbs (attached to prime mover)
M872A4 trailer 67,200 lbs (attached to prime mover)
M1074A1, M1075A1 PLS truck w/flatrack 32,250 lbs (40 psi max concentration)
M1076 PLS trailer 32,250 lbs (40 psi max concentration)
M1120 HEMTT truck w/flatrack 22,250 lbs (40 psi max concentration)
M984A4 HEMTT truck No secondary payload
M1077 flatrack (empty stacks) 4 high on PLS truck;
5 high on PLS trailer
M3 CROP flatrack (empty stacks) 6 high on PLS truck or PLS trailer

Make sure that any secondary general cargo loads fall under the approved vehicle or trailer payload capacity in the table above or contact Military Surface Deployment and Distribution Command Transportation Engineering Agency (SDDCTEA) for help.

Here's some additional helpful tips from the AAR OTLR that deserve spotlighting:
  • Visit the AAR OTLR library and download relevant volumes of the AAR OTLR manual HERE.
  • General cargo (palletized or crated cargo) must be restrained using approved AAR restraint devices of appropriate size and strength consisting of steel banding or chain assemblies that are properly marked. Rule 17 in Section 1 of AAR OTLR describes steel banding requirements. Rule 21 describes chain requirements.
  • Only use polyester web strapping for vertical restraint. Floor line blocking can be used on commercial flatcars. Note that nylon web strapping is not approved by the AAR.
  • For restraint calculations, check the table in Rule 5.4.3 of Section 1 in the AAR OTLR.
  • Always secure secondary general cargo directly to the primary cargo vehicle or trailer. Never apply rail chains from secondary loads directly to the railcar.
ISO Container Considerations
ISO (International Organization for Standardization) containers and PLS loads that are secured by authorized locks are acceptable, if they meet rail route clearance requirements and are within the acceptable payload rating of the primary cargo vehicle or trailer.
You’ll need to make sure that whenever secondary cargo is a shelter or container that all doors and hatches are properly secured. If not, equipment can slide out:
Ensure generator is properly pinned during rail transport
Ensure generator is properly pinned during rail transport
If the secondary cargo includes ammunition or explosives, then you’ll need to request additional guidance from the Explosive Safety Engineering Division at the Defense Ammunition Center HERE.
Small/Light Wheeled and Tracked Vehicles Need Testing
The AAR OTLR committee requires rail impact testing of vehicles and trailers transported as secondary loads (only a few trailers have been tested and approved as secondary rail loads and this type of shipping, in general, is limited).
If a small vehicle is secured as a secondary load for highway transport, that doesn’t mean it’s approved for rail transport. That’s because the amount of restraint needed for CONUS rail transport is three times greater than highway transport.
It’s important to note that PLS flatracks aren’t designed to handle concentrated loads of small vehicles and shouldn’t be used for secondary vehicle loads, unless tested and specified in an AAR OTLR’s loading figure.
CONUS and OCONUS Rail Systems
There are major differences in the CONUS and OCONUS rail systems. This means that secondary loads of certain vehicles could be allowed in Europe that wouldn’t be allowed in the US.
The securing of all equipment and vehicles is more stringent for CONUS rail transport than OCONUS. That’s because the US rail systems use automatic couplers to attach railcars, which rely on individual railcars hitting other railcars at about four (4) mph to couple them together. This impact-based system must be accounted for when securing both primary and secondary loads. OCONUS rail systems manually couple railcars together.
When a unit is returning to the US from an OCONUS deployment, the rail tiedowns of loads should be reviewed based on CONUS rail requirements. If there’s be a seamless transition to CONUS-based rail, then units should adhere to CONUS rail requirements, even when loading from their OCONUS location.
General Tips for Vehicles Shipped as Secondary Loads
You’ll need to coordinate with the rail carriers to ensure that they will accept vehicles as secondary loads. Likewise, you’ll need to contact the originating commercial rail carrier to inspect and measure the secondary loads to verify they fit within the required rail clearance “envelopes” for the desired rail routes.
Typically, any load that’s more than 11-ft wide or 11-ft tall will be checked by the originating rail carrier. Keep in mind that even smaller vehicles that are properly secured to cargo beds or trailers can create taller loads than you might expect.

WARNING - Vehicles as a secondary load must be secured with the correct size and strength tiedowns and chains approved by the AAR OTLR. It’s common for cargo trucks and trailers not to have the proper tiedowns or chains for rail load requirements.
The same directional restraint requirements from Rule 5.3.1 of Section 1 in AAR OTLR apply to vehicles as a secondary load. Also:
  • Restraints (chains) cannot contact any part of the vehicle except for the tiedowns (shackles or provisions) on the primary vehicle and trailer. That ensures the chains can be tightened to keep the secondary vehicle from buckling or breaking off during rail transport.
  • The primary and the secondary vehicles must have properly inflated tires.
Final Guidance

What if you don’t have access to the AAR’s OTLR manual, can’t find your specific vehicle or trailer in it or you just have questions and need more info? Contact the SDDC TEA at:

You’ll also find many useful resources on the SDDC TEA website HERE.
If you have petroleum and water assets, there’s helpful info for railcar operations planning and safety in the Petroleum and Water Organizations, Equipment Petroleum Platoon Leader, Rail Car Operations, and Unit Movements Smart Book (May 22). Grab your CAC and get it HERE.
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