We have looked at the different types of large trucks and the categories they fit into. The basic anatomy of these trucks and what makes them more of a challenge, and the statistics of how they travel, crashes, and how many travel our roads every day. Now, let us look at the different trailers that they pull, which can be a lot to look at. The pure number of different trailers and the cargo they haul can be quite overwhelming. A book could be written just to discuss this one topic.
There are some basic style trailers that we see the most of traveling up and down the highways. The flatbed trailer is a common one, used primarily in the construction trade. The good thing about these, for the most part, is we know what they are hauling. This also allows us to estimate the weight a little easier if needed. For example, a flatbed loaded with brick would weigh in around 38,000 to 40,000 pounds, not counting the trailer itself. Concrete pipe can weigh from 500 to over 1000 pounds each. These trailers also haul heavy equipment and machinery.
A front end loader, backhoe, or a large track backhoe can weigh quite a bit, and provide a tremendous challenge if sitting on another vehicle. I passed several flatbeds the other day hauling military Buffalo Armored vehicles, which with their heavy armor plating, weigh in at around 43,000 pounds. So even with the advantage of seeing what these trailers are hauling, the dynamics of a crash can be catastrophic. The straps used to hold down most of these loads are not designed to secure the load if the weight has shifted, and the load is now being applied differently than when it was secured. The other thing to consider is the condition of the straps and chains used to secure that load. With cost of trucking on the rise, and cutting and saving where you can, you can’t always depend on these folks using the best equipment.
Another trailer that is partially open is the dump trailer. These can be small to very large. Even though these trailers are open at the top, theoretically (covers are now supposed to be over the loads) we do not always know what they are hauling. Loads can vary from large to small stone, sand, construction debris, and asphalt. Can we really tell what these loads may weigh? Probably not. For example, a large tandem axle dump truck (with a floating axle), loaded with gravel, weighs about 38,000 pounds. The same truck carrying asphalt weighs only about 20,000 pounds. Most students in my classes think the asphalt weighs more than the gravel. These trailers can present a dilemma when they overturn and the weight is now displaced quite differently. This can destabilize the trailer from the truck and change the center of gravity and the forces now at work. Sometimes trying to lift or move part of the truck with the dump bed may look simple until you realize things are not moving as you thought they would. While doing a heavy vehicle class in Whiteville, N.C., the students found out that lifting a dump truck was not as simple as it appeared. They finally had to use a 20 ton hydraulic bottle jack on the rear knuckle of the truck to get the lift they wanted. But they worked through it, and all was good.
The box trailers present a totally unique problem because we have no clue what they are hauling or how much they weigh. These trailers are constructed with strong floor supports, because that is where the load is riding. The wall and roof support of the box trailer is not supportive, so there is not a lot of strength there. Once the trailer is on its side, the load will shift and the weight may now be resting on the side and roof supports. The problem may arise when you try and lift the trailer and the supports give way allowing the cargo to come “tumbling down.” This could be disastrous on the rescuers or the victims. Caution should be exercised when having to lift a box type trailer. The rear doors of these trailers are usually either bi-fold or roll-up. Again, if the load has shifted to the back and is resting against the rear door, extreme caution should be used.
We will look at some more types of trailers next time as we continue to explore the world of heavy vehicles. I hope everyone has a great summer, enjoy your vacation, catch some fish, and share time with the family. They are the backbone and support of what we do. Stay safe and always train hard and until next time, be the best you can be.