This Is What That Little Door On The Back Of Truck Trailers Is For (2023)

I think we’ve pretty well established that our readers spend a lot of time driving behind trucks, staring at the backs of trucks, and this meditative process of contemplating truckly posteriors naturally leads them to ask questions. Like why the quilted metal doors? Or, as I want to explore today, what’s the deal with that little, inset door on the back of some trailers, most often refrigerated trailers? Is it a pet door?


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If it is a pet door, are there truck cats?

Right up front I’m going to just tell you that, no, it’s not a pet door, and while there may be Trucker Cats, this little door is not for them. It was actually a bit tricky to confirm exactly what this door is for, because there seems to be two competing schools of thought about the door if you just try to Google it.


The first theory is that the door is used for inspecting the contents of the trailer, as explained by a number of internet people who claim to be truckers. Here’s one that explains how they use the door:

I’ve worked with refrigerated trailers for years and have never used it for any of the cited reasons. The main purpose as I see it is to check the status of the load without having to open the full door and losing temperature... I think the biggest reason is for a highway patrol or shipper/consignee to see if a trailer is loaded without losing temp in the trailer.



Huh. Okay. Another guy had a special name for it:

On refrigerated trucks and trailers, the small rectangular door is called a fruit door. It’s mainly used for temperature control and monitoring. It also can be used to help air out the trailer.

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Fruit door? That seems to be the only reference to it being called that, so I’m a bit skeptical.

Other sources also support this idea:

To view inside the trailer without opening the full access doors. used when container has a shipping tamper proof seal (manufacturers can tell if the large doors were opened when they should not have been).



This little door allows the driver to see how the pallets are stacked and the overall contents of the trailer without having to unseal the truck. It also prevents too much of the cool air to escape out of such a big door opening.


While this sounds plausible, especially the part about not wanting to open the full doors of the refrigerated trailer, which would waste energy and cause the trucker’s dad to pop up out of nowhere and yell “what are you trying to do, cool the whole neighborhood?” there’s still another explanation that needs investigating.

The other explanation is that the little door is used for ventilation purposes:

That is a vent door. There is usually one on the top front of the trailer as well. This is a reefer trailer. It is used for hauling refrigerated items and the interior has to be free of odor when loading at shipper. Usually, after hauling a meat load, the trailer will be washed at a trailer wash, then the vent doors are left open to allow quicker air drying and prevent mold or mildew.


This also seems plausible—you know how weird your fridge can end up smelling if you leave it off for a while, right? A refrigerated trailer is pretty much the same thing as a giant, wheeled fridge.

Other truck drivers supported this explanation, too:

These vent doors are sometimes used to allow air to circulate to dry out warming refrigerated trailers but can also be used on dry van trailers to provide air flow to non refrigerated produce (potatoes, onions, etc.) and plant (garden plants, trees, etc.) loads to prevent death and early spoilage caused by hot stagnant air.

There is one located at the top driver side at the head of the trailer as well as the rear passenger bottom as pictured here. The locations provide cross trailer airflow.

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There were many examples of both explanations online, so I realized it was time to stop seeing what randos on the internet thought, and to reach out to a real source to tell me what’s up with The Little Door: is it an inspection hole, or a vent? Or both?

I called a number of trucking companies and manufacturers of refrigerated trailers to find out. This actually proved a little trickier than I would have expected, since some companies were oddly unwilling to talk.


In fact, when I spoke with one company, a major manufacturer of refrigerated trailers, the person on the phone actually said this to me:

“You’re a journalist? I need you to tell me THE TRUTH about why you’re asking these questions.”


The person’s tone was quite hostile, like she was expecting me to say “we heard they were called devil doors and are used to poke children packed into the trailers for transport to Satanic rituals with harpoons” or something like that.

Eventually, though, I did get through to some experts, and I got my answer:

The door is called a Vent Door. It’s used for—you guessed it, ventilation.

I spoke with American Trailers of the Carolinas, manufacturers of many sorts of refrigerated trailers, and got a very good explanation.


The door at the back is paired with another one at the upper part of the front of the trailer, and when open, they provide flow-through ventilation. If you see a trailer driving with the little door open, I was told that most of the time that means the trailer is empty, the cooling unit is off, and it is being aired out for its next load.

I also asked them if the door was ever used for inspection, and was told it wasn’t, and then the American Trailers of the Carolinas employee used a pretty vivid example of why it’s useless for inspection:

“If you opened that door, what would you see? If the trailer is loaded, just a cardboard box. Maybe you could see where it said “DEL MONTE” or something. But you couldn’t see anything else. The whole front half of the trailer could be full of cocaine for all you could tell.”


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Damn, he’s right. It really wouldn’t be useful for inspection.

Next, I spoke with a person in the technical department of the same large manufacturer that was suspicious of me, as I mentioned earlier. To their credit, they decided I wasn’t writing a hit piece, and they had this employee contact me, on condition of anonymity, for some reason.


Whatever. The guy knew his stuff.

He confirmed it’s a Vent Door, used for ventilation, and also mentioned that they’re likely to be used for what’s known as “backhaul” loads, where the truck is filled with cargo to take back to its point of origin, so it’s not just being driven empty, which is wasteful.


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On a refrigerated truck, that backhaul load may not require refrigeration, so the cooling unit would be turned off. And, again, like your fridge when you turn it off, mold and mildew can grow and smell terrible, so to combat this, the vent doors are opened, and the trailer is aired out while hauling the non-refrigerated load.


I also asked our Secret Trucking Technician about the possible use of the door for inspection, and he also shot this down, adding that even if you wanted to, you really couldn’t since these doors have a stainless steel screen behind them.

Just to be safe, I spoke with another trucking firm, and they corroborated the story, leading me to confidently report to you that the little door is called a Vent Door, and it’s used for ventilation and airing out the trailer.


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If anyone claims to be a trucker and insist that it’s used for inspection or, worse, calls it a “fruit door,” you have my authorization to call them a moron who doesn’t know Jacqueline Squat about trucking.

Another mystery solved!


This Is What That Little Door On The Back Of Truck Trailers Is For? ›

Have you ever noticed a little door inside the bigger door at the back of a semi trucks trailer? The tiny door on a refrigerated trailer is called the vent door. It is screened and, along with a door at the front of the semi truck's trailer, is used to air the truck out whenever the refrigeration unit is turned off.

What is the little door on the back of semis? ›

This little door allows the driver to see how the pallets are stacked and the overall contents of the trailer without having to unseal the truck. It also prevents too much of the cool air to escape out of such a big door opening.

What is the flap on the back of a truck called? ›

The flaps on the back of a truck are called rear tail fairings, and they can help reduce drag on the vehicle. They may also catch any gravel or debris tossed back by the vehicle, potentially saving the windshields of anyone following behind.

Why do reefer trailers have a small door? ›

The small rectangular doors on refrigerated (reefer) units serve multiple purposes. They provide an easy way to check the interior temperature of the trailer when the doors are shut and also provide ventilation for loads that have high heat of respiration (such as produce).

What is a truck trailer door called? ›

Swing doors or “barn” doors are ubiquitous in the trailer industry. They are designed to maximize the net cargo area.

What is a swing door on a truck? ›

The swing door (or “barn” door) is infamous in the storage trailer industry. These doors are designed to maximize the net cargo area, requiring no internal housing in the truck, and allowing for the largest possible opening to the truck body.

Why do truck driver have a teddy in front of the truck? ›

Stuffed animals are found mostly on the trucks of men who perform hard, messy labor, which, despite the strength and bravery it demands, places them on the lower rungs of the ladder of occupational prestige. The motley animal, then, can function as a badge of outsider status, a thumbed nose to the squares and suits.

What are back flaps for? ›

A football back plate (sometimes referred to as a back flap) is a piece of safety equipment that attaches to a player's shoulder pads that helps protect the lower back. Back plates connect to the shoulder pads using an attachment strap and hardware/screws.

What is the bar on the back of a truck trailer called? ›

This steel barrier is known as a Mansfield bar, and it is designed to keep vehicles from going under the trailer in the event of a crash at the truck's rear end.

What is a Mansfield bar on a truck? ›

It's called a “Mansfield bar” or an “underride guard” and serves a very important function on the truck. This bar is meant to prevent cars from sliding underneath the trailer in the event of a rear-end collision.

What are small doors for on semi trailers? ›

Have you ever noticed a little door inside the bigger door at the back of a semi trucks trailer? The tiny door on a refrigerated trailer is called the vent door. It is screened and, along with a door at the front of the semi truck's trailer, is used to air the truck out whenever the refrigeration unit is turned off.

What is a roll door trailer? ›

Roll-up door trailers have a built frame, which allows these doors to slide up and down. This means that the door does not open outwards from the trailer, rather it rolls up to allow entry to the trailer. These are very useful for accessing tighter spaces for delivery, like in urban areas, and curbside deliveries.

What is a refrigerated semi trailer called? ›

In trucking, a “reefer” is a refrigerated trailer that gets attached to a semi-truck in order to transport perishables and other temperature-sensitive goods.

What are the different types of trailer doors? ›

In the semi-trailer storage industry, there are generally two types of doors: roll-up and swing doors. Each have their advantages and disadvantages.

What is a roll up door on a truck? ›

Aluminum roll-up doors (also called truck shutter doors) provide secure, convenient access to equipment compartments. Roll-up doors are used on delivery vehicles, cargo vans, emergency vehicles, fire trucks, service/work trucks, store fronts, and retail kiosks.

What is a truck slider? ›

These sliding windows, when making a comparison to other types of auto glass, most resemble a rear windshield. This provides a rear viewport for truck drivers whose passenger cabins are shorter than the typical passenger cabin of sedans, coupes, SUVs, and other vehicles.

What is a butler door? ›

A butler door is traditionally a full-sized single door that swings in and out with a double swinging hinge. Butler doors allow for the mess of a kitchen to be covered. Butler doors were once used to keep the kitchen staff from being visible to the dining room guests.

What is a door spreader? ›

The Door Buck Spreader* is a must have tool for any drywall installer. Eliminate the hassle of forcing wallboard behind door frames. The Door Buck Spreader* creates enough space to easily slide wallboard behind the door frame saving time and eliminating damage.

What is a load door? ›

A loading bay door is a door at the entrance or exit point in a commercial or industrial building where the goods are loaded or unloaded from the trucks.

Why do truckers sleep with their trucks running? ›

Truckers rely heavily on truck stops as a safe place to park their vehicles overnight or when they need to take a rest break. Long haul truck drivers generally sleep in their trucks, as they may be away from home for days or even weeks at a time.

What do truck drivers call their trucks? ›

Rig—a trucking term used for big trucks and tractor trailer units.

What is the bar on the back of a semi trailer? ›

Mansfield bars, also known as underride guards, are metal bars affixed to the back of semi trucks and trailers. They're meant to supplement a bumper and prevent passenger cars from sliding underneath semi trucks in the event of a collision.

Why do trucks have bars on the back? ›

Those steel bars hanging from the truck's platform bed are known as a “rear underride guards” or “rear impact guards.” They are designed to prevent vehicles from sliding underneath a trailer during a rear-end collision. Unlike your average car, truck trailers and straight trucks do not have rear bumpers.

What is the purpose of rear mud flaps? ›

Mud Flaps protect your vehicle by safely deflecting road debris away from the fender wells. Your tires are in constant contact with a long list of obstacles ranging from muddy water to thick tar on a daily basis. Fender wells are made to contain these elements, but need some additional help.

What is a tailgate on a semi-truck? ›

A tailgate (Canada) or liftgate (USA) is a platform at the truck's rear, used in LTL shipping for unloading freight.

What is it called on the back of a semi-truck? ›

Trailer. The trailer section of a semi-truck latches onto the rear of the tractor unit and stabilizes it for large, heavy loads. Though the type of trailer transported can vary depending on the type of cargo the driver hauls, every trailer unit contains cargo space, a landing gear, and tandem axles.

What is the purpose of roll up doors? ›

Rollup doors are steel doors that roll up into a coil directly above the opening. As they protect against unwanted entry and natural elements, they are indispensable for many businesses.

What is the purpose of rolling doors? ›

A rolling steel door is a coiling door that's typically used in commercial and industrial applications - from warehouses and loading docks to freight terminals and distribution centers. They're constructed of galvanized steel slats that interlock to form one strong and continuous curtain.

What is a lifting door? ›

This door system utilizes an overhead or floor mounted drive unit with counterweight support that vertically lifts and stacks the doors above the door opening. This can be operated with the counterweight or electrically.


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