What Is The Little Door On The Back Of Semi Trailers For?
We've all found ourselves stuck behind a slow-moving semi-truck before, either in tight city traffic or on the highway. Every time it happens, we're left staring at the massive trailer in front of us, which may lead to you wondering what the little door on the back is for. It can't be used for loading or unloading, so what purpose does it serve?
According to Central California Truck and Trailer Sales, the door on the back of semi-trailers is used for ventilation and can often be found on refrigerated trailers, or "reefers." When opened, the load can get proper ventilation while the truck is in motion. There's also a door on the front of the trailer, which can be opened to provide better airflow throughout the trailer.
While ventilating a refrigerated load seems counterproductive, it's highly effective when hauling fresh produce. Onions, for example, would need ventilation despite the length of the trip. Ensuring proper ventilation not only protects the cargo, but the drivers who are held responsible for the condition of the contents they're transporting.
False rumors surround the little door on the back of semi trailers
The little door on the back of a semi-trailer is mostly used for ventilation, but does the door serve any other purpose?
According to a 2022 article published by MotorBiscuit, a transportation content website, the door is opened when the refrigerated trailer is turned off. This allows the trailer to air out, preventing mildew and mold from growing inside. In a 2021 piece by Jalopnik, there are rumors that the door is also used for inspection, though that rumor doesn't make much sense, as looking into a full trailer wouldn't yield much information. Plus, anything loaded beyond the line of sight wouldn't be visible.
However, there are some things that the little door can't do. Hale Trailer Brake & Wheel, a new and used equipment dealer operating on the East Coast, pointed out that even venting won't always protect cargo. The more extreme the temperature is one way or the other, the more likely it is that electronic items could be damaged or foods can go bad.