# What the Heck Is It?! (semi trailer design) **URL:** \ **Category:** Factual Questions\ **Created:** [May 2, 2022, 12:12pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803 "2022-05-02T12:12:07Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 12:12pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/1 "2022-05-02T12:12:07Z")
My question is regarding a semi’s trailer design. First of all, it is a full semi trailer and not something that is shipped via railroad and bolted to a trailer frame. Second, I see them every day, so this design is not a rarity by any means. Before you ask why in the world I simply didn’t post a picture of what is confusing me, let me say I searched mightily but simply couldn’t find one. So, I’ll do my best to describe it. Okay, imagine your standard “box” design for a trailer. Now, remove the roof and remove the back doors so that the entire top and back are completely open. Now, permanently bolt a ladder to the middle of the back from the base to the frame running across the top. This “ladder”, if that is what it really is, not only blocks the free access to the back of the box because it is positioned smack dab in the middle, but it leads to the top of … NOTHING. There is no roof to stand on. The open top would be totally understandable if one were dumping rocks/soil, garbage into it with heavy equipment, but that can’t be the case because it has no back. The stuff would just run out onto the highway. So, what exactly is the purpose of this design?! ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 2, 2022, 12:28pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/2 "2022-05-02T12:28:41Z")
Like this? [![](https://blog.crtsinc.com/hs-fs/hubfs/Logging%20Ad%20Chip%20Van.jpg?width=400&name=Logging%20Ad%20Chip%20Van.jpg) ](https://blog.crtsinc.com/hs-fs/hubfs/Logging%20Ad%20Chip%20Van.jpg?width=400&name=Logging%20Ad%20Chip%20Van.jpg) [![](https://dygtyjqp7pi0m.cloudfront.net/i/14562/15739451_2.jpg?v=8CFE8172C87FA10) ](https://dygtyjqp7pi0m.cloudfront.net/i/14562/15739451_2.jpg?v=8CFE8172C87FA10) > **[Peerless Trailers: The Toughest Trailer in the Timber Industry](https://blog.crtsinc.com/peerless-trailer-spotlight)** > > CRTS carries new & used Peerless Open Top and Inwards Chip Trailers, including trailers with customizations like Drop Center Configuration or a Live Floor. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 12:42pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/3 "2022-05-02T12:42:50Z")
That’s pretty much it except that there are no extra bars going from the base to the top frame, just that ladder thingy bolted right in the middle. Also, they don’t have the front part of the trailer that almost touches the ground. Timber, you say? In Chicagoland? The ones I’ve seen are always empty which, I guess, is why I have never known what they are for. Thank you for responding! ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 2, 2022, 12:48pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/4 "2022-05-02T12:48:55Z")
Seems they are a chip trailer and loaded like this: [![](https://www.modsls17.com/wp-content/uploads/2020/10/2020-dorsey-chip-trailer-v1-0-0-0-mod-3.jpg) ](https://www.modsls17.com/wp-content/uploads/2020/10/2020-dorsey-chip-trailer-v1-0-0-0-mod-3.jpg) I assume Chicago has need of wood chips for gardens or something. Interesting how they are unloaded: [![](https://i.pinimg.com/originals/c7/15/c9/c715c9d8446e32d1e9ee62b4f5a6a040.jpg) ](https://i.pinimg.com/originals/c7/15/c9/c715c9d8446e32d1e9ee62b4f5a6a040.jpg) ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 12:53pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/5 "2022-05-02T12:53:12Z")
Why aren’t the chips pouring out of the back of the open trailer? ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 2, 2022, 12:57pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/6 "2022-05-02T12:57:50Z")
It’s a mesh screen, it’s not an open space. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 12:58pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/7 "2022-05-02T12:58:59Z")
Ah, so that’s something they attach and wouldn’t be visible when the trailer is not in use. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 2, 2022, 1:00pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/8 "2022-05-02T13:00:12Z")
I’m assuming it’s always there and you’re just not seeing it. There’s no reason to take that off. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 1:02pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/9 "2022-05-02T13:02:03Z")
If i ever see one parked, I’m going to walk up to the back and look inside! LOL ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [May 2, 2022, 1:33pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/10 "2022-05-02T13:33:05Z")
**Moderator Note** Title edited to more clearly indicate the topic. Please do not use vague titles. ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [May 2, 2022, 1:45pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/11 "2022-05-02T13:45:06Z")
I thought this was going to be about those semis that have the three giant triangle containers for a trailer. I’d like to know what that is. ---
**Author:** ![DorkVader](https://avatars.discourse-cdn.com/v4/letter/d/73ab20/32.png) [@DorkVader](https://boards.straightdope.com/u/DorkVader)\ **Post date:** [May 2, 2022, 2:02pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/12 "2022-05-02T14:02:21Z")
Are you talking about the triangle being on its point with the broad base up on top? Those are bottom dump [trailers](https://duckduckgo.com/?q=bottom+dump+trailer&t=iphone&iax=images&ia=images) or perhaps like [this?](https://images1.farms.com/ufe-images/files/dealers/longhaul-trailer-sales/listingimages/65490-1.jpg) There is another variety for liquids, or finer grained solids that can flow like a liquid (sand, or fine silt or flour[well not flour but fine like that] or whatever) but I can’t seem to get google to bring up a picture of one those for me. Edit; found one, its a dry bulk pneumatic trailer, I can’t seem to get a link to work for the one I found, but if you go to trailers of texas dot com, they have pics of them ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [May 2, 2022, 2:22pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/13 "2022-05-02T14:22:13Z")
Yeah kind of. It’s three triangle containers with the base at the top, and it’s completely closed in. It seems like it’s hauling a chemical to me. But why triangles instead of a cylinder? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 2, 2022, 2:22pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/14 "2022-05-02T14:22:47Z")
> [@DorkVader](#): > > Edit; found one, its a dry bulk pneumatic trailer, I can’t seem to get a link to work for the one I found, but if you go to trailers of texas dot com, they have pics of them Like this? [![](https://d2uhsaoc6ysewq.cloudfront.net/1711/Dry-Bulk--Pneumatic-Tank-Trailers-Polar-940-Cu-Ft-2-Hopper-28300636-thumb.jpg) ](https://d2uhsaoc6ysewq.cloudfront.net/1711/Dry-Bulk--Pneumatic-Tank-Trailers-Polar-940-Cu-Ft-2-Hopper-28300636-thumb.jpg) Or… [![](https://d2uhsaoc6ysewq.cloudfront.net/1711/Dry-Bulk--Pneumatic-Tank-Trailers-Tremcar-1625-cu-ft-Vac-25526537.jpg) ](https://d2uhsaoc6ysewq.cloudfront.net/1711/Dry-Bulk--Pneumatic-Tank-Trailers-Tremcar-1625-cu-ft-Vac-25526537.jpg) ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [May 2, 2022, 2:23pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/15 "2022-05-02T14:23:55Z")
Yeah, that’s it. Thanks ---
**Author:** ![Sunny\_Daze](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunny_daze/32/438_2.png) [@Sunny\_Daze](https://boards.straightdope.com/u/Sunny_Daze)\ **Post date:** [May 2, 2022, 2:26pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/16 "2022-05-02T14:26:06Z")
I also see something similar to the trailer described for the transportation of certain kinds of produce, garlic comes to mind. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 2:44pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/17 "2022-05-02T14:44:42Z")
Ah, “pneumatic” translates to forced air emptying the contents from the tanks. Lucky I saw this here now, otherwise I would have been back with another question! ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 2, 2022, 3:36pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/18 "2022-05-02T15:36:00Z")
> [@Jasmine](#): > > Ah, “pneumatic” translates to forced air emptying the contents from the tanks. They’re for viscous powdery solids like cement and flour. They tend to clump and hang up and refuse to empty. Ever been in the bottom of a silo that has a big wad of sawdust or whatever overhead, and it’s just suspended in the air, held in place by cohesion? If you ever find yourself in that spot, get out! The whole thing could WOOF down on you at once. Anyway, they use air to empty these trailers. And they all have decals that say “do not bang on sides of trailer”. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 2, 2022, 3:42pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/19 "2022-05-02T15:42:03Z")
> [@Just\_Asking\_Questions](#): > > If you ever find yourself in that spot, get out! Yes, people have actually been killed (suffocated) in that way. In fact, the 1985 Harrison Ford movie, “Witness”, had Ford offing one of the bad guys in just that manner. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 2, 2022, 3:48pm UTC](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803/20 "2022-05-02T15:48:19Z")
> [@Jasmine](#): > > Yes, people have actually been killed (suffocated) in that way. The one I saw was so plugged, the workers were poking at it with long sticks, trying to start a small flow that would progress to a large flow, but without bringing the whole thing down at once. i was too young to know how dangerous what they were doing was. Other than setting off a small explosive, though, I don’t know what else you could do. Working it from the top is equally as bad. coda: that silo later burned down. Took the whole building with it. At least no one got killed. [Next page](https://boards.straightdope.com/t/what-the-heck-is-it-semi-trailer-design/963803.md?page=2)